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(共41张PPT)
Unit 4 The Wonders of Nature
Revision 单元复习课
（人教版2024）八年级英语
下
学习目标
能听懂有关介绍自然奇观等地理事物的语言材料并能向他人介绍自然奇观并分享对不同自然奇观的看法。
一
能够读懂介绍自然奇观等地理事物的语篇，并能识别图片中不同的自然奇观。
二
了解我国和世界的一些自然奇观；了解珠穆朗玛峰及人类克服困难、挑战极限的精神；热爱祖国的大好河山，增强自豪感。
三
能找出语篇中特定信息，能提取、概括语篇中各段落的关键信息和主要内容，能根据语篇推断人物的心理和语篇的深层含义。
四
能借助网络平台，通过查询比较，加强对中国以及世界地理知识的了解；能用寻读法搜寻与片中的特定信息。
五
单元知识图谱
Time to relax
短语
动词
名词
形容词/副词
measurement,level,surface,depth,vessel,bottom,waterfall,
civilization,means,development,desert,mile,pool,climber,distance,condition,degree,cliff,death,teamate,shoulder,ladder,curiosity,
wonder,dive,research,survive,measure,risk,attract
单词
unusual,cubic,changeable,successfully,simply,southern,risky,located,
freshwater,curious,natural,underwater,natural,northeastern,alive,
句型
4.If you visit it,you will see the largest living structure on earth.
5.Mountain climbers even called that way the “Death Road”,but a Chinese climbing team was determined to make the climb.
1.The Yellow River is 5,464 kilometres long and is the second longest.
2.It is about 9,000,000 square kilometres in size.
3.The Yangtze River travels the farthest in China and is about 6,300 kilometres long.
The Wonders of Nature,geography facts,natural wonders,Nile River, Dead Sea,Sahara Desert,deep sea,deepest dive of a whale,deep-sea researcher,Yellow River,Yangtze River, ancient civilizations mother,Victoria Falls,greatest wonders, terrible conditions,thin air,
语法
1.形容词/副词的比较级与最高级
2.大数的表达
写作
英语短文：自然景观
核心词汇
1. ______n.奇观；惊叹 v. 想知道；感到诧异2. __________n. 数量；测量
3. ____prep. 少于；低于 adv. 在（或到）下面4.______ n. 高度；水平；程度
5.______n. 表面；表层6.______ n. 深（度）；纵深7. ____v. & n. 潜水；跳水；8.______ v. & n. 研究；调查9.______n. 大船；轮船10.______ adj. 特别的；11______ n. 底部；最下部12. ______n. 瀑布13. _________n. 文明
14._____n. 沙漠；荒原15. _____adj. 立方的16. ______n. 英里
17. ____n. 池塘18.________n. 攀登者19.________adj. 北部的；向北的
20.______ n. 距离；遥远 21.______ v. 生存；存活；艰难度过
22.______ n. 状态；境况23.______ n. 度；度数；程度24. ______n. 悬崖25.__________ adj. 可能变化的；常变的26_______ n. 死亡；破灭
wonder
measurement
below
level
surface
depth
dive
research
vessel
unusual
bottom
civilization
waterfall
desert
cubic
mile
pool
climber
northern
distance
survive
condition
degree
cliff
changeable
death
核心词汇
27._________adj. 有决心的；坚决的28_______ n. 同队队员；队友
29._________n. 肩膀；肩部30.________n. 梯子；阶梯；途径
31_________v. 测量 n. 措施32.___________adv. 成功地；顺利地
33.________v. 使……冒风险n. 危险；风险34._________n. 好奇心；求知欲
35._________n. 追求的目标；野心；雄心36.________n. 探险者；勘探者
37._________adv. 仅仅；只；简单地38._________adj. 有危险（或风险）的
39._________adj. 南部的；向南的40._________adj. 位于；坐落在
41._________adj. 淡水的的42._____n. 类型；种类43._________v. 吸引；44._____adj. 好奇的；求知欲强的45._____adj. 自然的；天然的46._________adj. 水下的 adv. 在水下47._________adj. 东北的；东北方向的48.____n. 海岸；海滨49._____n. 礁；礁脉50._________n. 结构（体）；构造
determined
teammate
measure
ladder
southern
curiosity
shoulder
successfully
explorer_
risk
ambition
risky
simply
type
freshwater
located
northeastern
underwater
natural
curious
attract
reef
coast
structure
核心词汇(词性转换)
wonder n. 奇观；惊叹；v. 琢磨；想知道；感到诧异 →________ adj. 精彩的；绝妙的
depth n. 深（度）；纵深 → _______adj. 深的；adv. 深深地 →_______v. 加深；深化
dive v. & n. 潜水；跳水；俯冲 → _______n. 潜水员；跳水运动员
research v. & n. 研究；调查 → _________n. 研究者；调研人员
unusual adj. 特别的 → _______ adj. 通常的；平常的 → _______ adv. 通常；平常
development n. 发展；壮大 →_______ v. 发展；开发 →_______ adj. 发达的；成熟的 →_________adj. 发展中的
climber n. 攀登者；登山者 →_______v. 攀登；攀爬 → _______ n. 攀登（运动）；登山（运动）
northern adj. 北部的；向北的 → _________ n. 北；北方；adj. 北方的；adv. 向北
natural adj. 自然的；天然的；天生的 → _________n. 自然；天性
wonderful
deepen
deep
researcher
diver
usual
usually
developing
developed
develop
nature
north
climbing
climb
核心词汇(词性转换)
10.distance n. 距离；遥远 → ________adj. 遥远的；远处的
11.death n. 死亡；毁灭；破灭 → ________v. 死亡；消逝 →________ adj. 死的；无生命的 →
12.determined adj. 有决心的；坚决的 →________ v. 决定；确定 → ________ n. 决心；果断
13.successfully adv. 成功地；顺利地 → ________ v. 成功；达成 → ________n. 成功；成就 →________ adj. 成功的；有成效的
14.curiosity n. 好奇心；求知欲 →________ adj. 好奇的；求知欲强的
15.simply adv. 仅仅；只；简单地 → ________adj. 简单的；单纯的
16.located adj. 位于；坐落在 →________v. 定位；位于 →________ n. 位置；地点
17.attract v. 吸引;引起→ ________ n. 吸引力；景点 →________ adj. 有吸引力的；迷人的
distant
dead
die
successful
determine
success
succeed
determination
curious
attractive
attraction
location
locate
simple
核心短语
根据汉语写出对应的英语短语
1. 自然奇观 2. 地理事实
3.尼罗河 4. 珠穆朗玛峰
5. 死海 6. 撒哈拉沙漠
7. 马里亚纳海沟 8. 深海
9. 鲸鱼最深潜水记录 10. 黄河
11. 古代文明
12. 长江 13.母亲河
14. 维多利亚瀑布 15. 稀薄的空气
16. 高悬崖 17. 多变的天气
18.中国登山队 19. 淡水湖
20. 大堡礁 21. 盐湖
The Wonders of Nature
geography facts
Mount Qomolangma
Dead Sea
Nile River
deepest dive of a whale
deep sea
Sahara Desert
Yangtze River
ancient civilizations
Yellow River
thin air
Victoria Falls
mother river
changeable weather
high cliffs
salt lake
Great Barrier Reef
freshwater lake
Chinese climbing team
Mariana Trench
将下列短语与汉语意思相匹配
自然奇观
尼罗河
珠穆朗玛峰
死海
撒哈拉沙漠
马里亚纳海沟
古代文明
维多利亚瀑布
稀薄的空气
淡水湖
大堡礁
盐湖
核心短语
Nile River
Dead Sea
Victoria Falls
Mariana Trench
Great Barrier Reef
Sahara Desert
ancient civilizations
salt lake
Mount Qomolangma
thin air
freshwater lake
The Wonders of Nature
核心词汇
词汇解析:wonder
词性 词义 例句
n. [C]奇 观 ； 奇迹 The Grand Canyon is one of the natural wonders ofthe world.科 罗拉多大峡谷是世界自然奇 观之一。
[U]惊叹 The sight of the Great Wall filled me with wonder.
看见长城，我惊奇不 已 。
v. 琢磨；想知道 （=want to know） If you study physics,wonder why light travels faster than sound.如果你学习物理，你会想知道为 什么光比声音传播速度快。
感到诧异 I wondered at her beautiful singing.
她优美的歌声让我惊讶
核心词汇
词汇辨析：在……下边
单词 意思辨析 例子 反义词
below 表示在某物的下方，但 不一定是在正下方。 416 metres below sea level 低于海平面 416米
above
under 表示在某物的正下方。 under my umbrella 在伞下边 over
核心词汇
词汇解析:experience
词性 意思 例句
n. [C](一次)经历，体验 Tom likes traveling. He has many unusual experiences.汤姆喜欢旅游，他有许多不寻常的经历。
[U]经验 Mrs Green has a lot of teaching experience.格林老师有着丰富的教学经验
v. 经历 Children need to experience things for themselves to learn.
儿童需要通过亲身经历来学习。
考点链接
In April, the weather in some places in Hubei is really changeable. people may _____ four seasons in one week.
A. organize B.describe C. check D. experience
核心词汇
词汇解析：方位词
northern:北方的，北部的
由 “north(n. 北；北方)+-ern” 构成。表示方位的名词在词尾加-erm可构成形容词，常见的还有：
east+ern→eastern（东方的，东部的）
west+ern→western(西方的，西部的）
south+ern→southern（南方的，南部的）
其他方位词：
核心词汇
词汇辨析
单词 词性 词义 用法
death n. 死亡 在句中作主语或宾语。
die v. 死 在句中作谓语，为非延续 性动词，不能与表示一段 时间的状语连用。
dead adj. 死的 作定语或表语，表状态。 be dead可与一段时间连用。
dying adj. 临终的 在句中作定语。the dying“临终者，垂死者”
语境串记
The old man lies in bed,thinking of his dead army comrades.They died for the liberation of the people.It is a worthy death. His dying wish is to see his living army comrades.
这位老人躺在床上，想起他死去的战 友。他们为人民的解放事业而死，死得其所。他的 临终心愿是去看看他仍然健在的战友。
核心词汇
词汇辨析
单词 词义 两物体间的关系 反义词 例句
above 在……上面 不接触，不一定 垂直 below He lifted his hands above his head. 他双手举 过头顶 。
over 在……正上方 不接触，垂直 under There is a bridge over the river.
河上有座桥。
on 在……上面 有接触面 beneath He put the book on the desk. 他把书放在了书 桌上 。
under
on
beneath
above
below
over
核心词汇
针对训练
用括号内所给单词的适当形式填空
1.(2025山西中考改编)Xuankong Temple is one of China’s ________(wonder).
2.(2025山东临沂中考改编)Nowadays, great inventions make our lives better in ____________(amaze) ways.
3.(2024西藏中考改编)Human beings should get along well with ______ (natural).
4.Among all the cinemas, Movie World sells the tickets at the ________ (low) price.
5.The Caspian Sea is the ____________ (large) of all the salt lakes.
wonders
amazing
nature
lowest
largest
重点句型
1.The Yellow River is 5,464 kilometres long and is the second longest.
黄河全长5464千米，是第二 长 河
the+序数词+形容词最高级(+可数名词单数)第几……的(……)
2.It is about 9,000,000 square kilometres in size.
它的面积约为900万平方千米。
“基数词+square+单位词+in size”面积为……
3.The Yangtze River travels the farthest in China and is about 6,300 kilometres long.长江是中国流程最 远的河流，全长约6300千米。
“基数词+单位词+形容词”表达物体的长、宽、高、深等
→ 当基数词大于1时，单位词要用复数形式
重点句型
4.If you visit it,you will see the largest living structure on earth.
如果你参观它，你会看到地球上 最大的生物结构。
这是一个条件状语从句。
主句：you will see the largest living structure on earth, 其中you 作主语， will see 作谓语； the largest living structure 作宾语。
从句：If you visit it, 其中If 是引导词； you作主语； visit作 谓 语 ；it作宾语。
5.Mountain climbers even called that way the “Death Road”,but a Chinese climbing team was determined to make the climb.登山者们甚至将那条路线称为“死亡之路”,但一支中国登山队决心要完成这次攀登。
本句是由but连接的并列转折句，前后时态要保持一致，本句均为过去时。
be determined to do sth.决心做某事
e.g:I’m determined to succeed.我决心要获得成功。
并列连词，表转折
if引导的条件状语从句
重点句型
6.People said（that） it was so high that even birds could not reach it
人们说它高得连鸟儿都飞不到。
句子结构：主语谓语 省略引导词that的宾语从句(含so...that...引导的结果状语从句，意为如此……以至于……)
结果状语从句
宾语从句
7.Bit by bit,the climbers pulled themselves up,and they made it past the Second Step.登山者们一点一点地奋力往上攀爬，最终成功越过了第二 台阶。
这是一个并列句，由并列连词 and 连接两个独立分句。
第一个分句：主语是 the climbers; 谓语动词 是 pulled…up; 宾语是themselves 。
第二个分句：主 语是they; made 作谓语； it 作宾语。
归纳拓展 该句的结构为：简单句+并列连词and+ 简单句。 符合此结构的并列连词常见的还有but (但是) ,or (或者； 否则),yet (然而；但是)
重点句型
针对训练
根据汉语意思完成句子,每空一词
1.这个湖有多深 ________ _________ is the lake
2.请尽可能快地完成作业!
Please finish your homework_______ ____________ _______ you can!
3.地球上最深的点是哪里 Where’s _____ _______ ______ on earth
4.这艘科研船比许多其他船只下潜得更深。
This research ___________ __________ deeper than _________ ___________.
5.地壳的不同部分承载着山脉和海洋。
Different __________ of the earth’s crust __________ mountains and oceans.
　How deep
　as quickly as
　the deepest point
　vessel dived many others
　parts carry
单元语法
（一）形容词/副词的比较级与最高级
1.定义：
比较级：用于两者之间的比较，常与 “than” 连用，描述自然奇观在 “高度、深度、面积”等维度的差异。
例：The Yangtze RiverA is longer than the Yellow River in China.长江比中国的黄河长。
The Mariana Trench is deeper than any other part of the ocean.马里亚纳海沟比海洋其他任何部分都深。
最高级：用于三者及以上的比较，常与 “the” 连用，后接 “in/of” 短语限定范围，强调自然奇观的 “极致特征”。
例：Mount Qomolangma is the highest mountain in the world. 珠穆朗玛峰是世界最高峰。
The Sahara Desert is the largest hot desert in the world. 撒哈拉沙漠是世界最大的热沙漠。
单元语法
比较级构成规则 最高级构成规则 例词
①一般词尾直接+er ①一般词尾直接+est smart→smarter→smartest（最聪明的）
fast→faster→fastest（最快的）
②以不发音的“e”结尾，词尾+r ②以不发音的“e”结尾，词尾+st wide→wider→widest（最宽的）
large→larger→largest（最大的）
③“辅音字母+y”结尾，变y为i+er ③“辅音字母+y”结尾，变y为i+est happy→happier→happiest（最开心的）
easy→easier→easiest（最容易的）
④重读闭音节且末尾只有一个辅音字母，双写辅音字母+er ④重读闭音节且末尾只有一个辅音字母，双写辅音字母+est thin→thinner→thinnest（最瘦的）
fat→fatter→fattest（最胖的）
⑤部分双/多音节词，原级前+more ⑤部分双/多音节词，原级前+most carefully→more carefully→most carefully
important→more important→most important
（一）形容词/副词的比较级与最高级
单元语法
（一）形容词/副词的比较级与最高级
原级 比较级 最高级 单元应用场景
good/well better best The Great Barrier Reef is one of the best places to study marine life.
bad/badly worse worst The weather on Mount Qomolangma can get worse quickly.
many/much more most The Amazon Rainforest has the most variety of plants and animals.
little less least The Dead Sea has less oxygen than other seas, so few fish live there.
3.不规则变化
单元语法
（一）形容词/副词的比较级与最高级
4.用法
①比较级前加修饰语（much/a lot/a little/even等，表程度）
例：This bag is much bigger than that one.这个包比那个大得多。
②“越来越……”（结构：比较级+and+比较级；多音节词用more and more+原级）
例：The tree is growing taller and taller.树长得越来越高。
Our city is becoming more and more modern.我们的城市变得越来越现代化。
③ “越……，越……”（结构：the+比较级, the+比较级）
例：The harder you study, the better grades you will get.你学习越努力，成绩就越好。
④原级比较：两者“一样……”（结构：as+原级+as）
例：Tom is as tall as Jim.汤姆和吉姆一样高。
单元语法
（一）形容词/副词的比较级与最高级
4.用法
⑤一方“不如”另一方（结构：not as/so+原级+as）
例：This book isn’t as interesting as that one.这本书不如那本有趣。
⑥“最……之一”（结构：one of the+最高级+可数名词复数）
例：Beijing is one of the most beautiful cities in China.北京是中国最美丽的城市之一。
⑦“第几最……”（结构：序数词+the+最高级）
例：She is the third shortest girl in her team.她是她队里第三矮的女生。
⑧比较级与最高级互换
例：Lily runs faster than any other
单元语法
（二）大数的表达
中文 英文 数字表示
百 hundred 100
千 thousand 1,000
百万 million 1,000,000
十亿 billion 1,000,000,000
万亿 trillion 1,000,000,000,000
读法规则：
325=three hundred and twenty-five
1500= one thousand five hundred(正式)/fifteen hundred(非正式，更常用)；
1001=one thousand one 10,000 = ten thousand
1,000,000 = one million 3.14=three point one four
1,234,567=one million two hundred thirty-four thousand five hundred and sixty-seven
复合表达：“数字+单位+形容词”，
如8,848.86 metres high 8848.86米高、416 metres below sea 低于海平面416米

单元语法
针对训练
Ⅰ.写出或拼出数字
1.Mount Qomolangma is about _____________ (eight thousand, eight hundred and forty-eight) metres high.
2.The Mekong River is about _____________(four thousand, eight hundred and eighty) kilometres long.
3.The Great Barrier Reef(大堡礁) covers an area of _______________(three hundred and forty-five thousand) square kilometres.
4.The Sahara Desert covers an area of about 9,000,000 (_______________) square kilometres.
5.The average depth of the Pacific Ocean is about 4,280 (_________________________________) metres.
nine million
345,000
4,880
8,848
four thousand, two hundred and eighty
单元语法
针对训练
Ⅱ.用括号内所给单词的适当形式填空
6.My home is the closest to school while Jim’s is the ____________________ (far).
7.(2025福建中考改编)AI technology in China has developed _____________(fast) than anyone expected.
8.Do you think what the ____________ (deep) sea in the world is
9.(2024甘肃白银中考)Actions speak ___________ (loud) than words.
10.Some blind animals can“see” as _________(good) as others.
　well
　louder
　deepest
faster
　farthest/furthest
主题写作
一、单元话题：本单元的主题是“自然奇观”,要求学生能够通过列数字、作比较等写作手法,向读者介绍一种自然景观。与此相关的主要写作维度有:①介绍自然奇观的基本信息;②运用数据对比突出其“独特性”;③描述人类与自然奇观的互动;④呼吁敬畏与保护自然。
二、写作要求
1.围绕一处自然奇观展开，明确说明该奇观的名称、地理位置及核心特征(如高度、 面积、独特景观等)。
2. 结合单元主题“探索自然”,重点描述该奇观的神奇之处及给你的感受，可适当提及 人类与自然的联系。
3. 正确使用比较级、最高级形容词/副词及大数表达等单元语法知识，语言生动，逻 辑清晰。
4. 字数不少于80词，文中不得出现真实人名、校名。
自然景观
写作指导
1. 结构设计：采用“奇观介绍一细节描述一感受感悟”的三段式结构，先明确奇观基本信息，再聚焦其独特性，最后升华对自然的认知。
2. 内容要点：
· 基础信息：明确自然奇观的类型(如山脉、河流、沙漠、湖泊等)、位置及关 键数据(如珠穆朗玛峰高8848.86米、撒哈拉沙漠面积约900万平方公里), 体现大数表达的单元重点。
· 特色描述：结合感官体验或科学事实，描述奇观的独特之处(如“峰顶常年积 雪”“河水呈黄色因携带泥沙”“深海动物能发光”),可使用比较级/最高级(如 "the highest mountain"“the deepest trench”)。
· 情感与联系：阐述奇观带来的震撼感受(如“感到人类的渺小”“赞叹自然的伟 大”),可提及人类对自然的探索(如中国“奋斗者”号深潜)或保护的重要性， 呼应单元“人与自然连接”的主题。
写作模板
开头段 Among all the natural wonders in the world, ___________ (自然奇观名称)impresses me most.It is located in __________(地理位置如) and is famous as __________ (核心称号，如 "the highest mountain in the world""the largest coral reef system").
中间段 This wonder is full of amazing facts.First,its________( 特征1, 如 "height""area") is surprising—it reaches ________ ( 具体数据,如8,848.86 metres high"“345,000 square kilometres”). Besides,it has unique ________ ( 特征2 ): ________ ( 具体描述,如 “the peak is always covered with snow""thousands of colourful fish live in the clear water").What's more, ________( 人 类与自然的联系,如 "Chinese climbers reached its top in 1960""scientists are working to protect it from pollution”)shows our connection with nature.
结尾段 Visiting or learning about this wonder makes me feel ________(感受).It teaches me that nature is both powerful and fragile.We should ________(行动倡议)so that future generations can also enjoy their beauty.Nature's wonders are gifts we should cherish forever.
主题写作范文
A Natural Wonder That Impressed Me\
Among all the natural wonders in the world,Mount Qomolangma impresses me most.It is located on the border of China and Nepal and is famous as the highest mountain in the world.Learning about it makes me feel the magic of nature deeply.
This wonder is full of amazing facts.First,its height is surprising—it reaches 8,848.86 metres,and scientists say it is still growing taller.Besides,it has harsh but unique conditions:temperatures can drop to -30 degrees,and climbers have to fight against thin air and changeable weather.What's more,Chinese climbers made history here—they first reached the top from the northern "Death Road"in 1960 and measured its height accurately in 2020.Their spirit of exploration inspires me a lot.
Visiting Mount Qomolangma is my dream.It teaches me that nature is both powerful and respectful.We should protect such wonders so that they can keep amazing the world.After all,nature's greatness lies not only in its size but also in the connections it builds with humans.
综合训练
Ⅰ.用括号内所给单词的适当形式填空
1.The sign says the area is __________ (risk), so we shouldn’t go there.
2.Lots of tourists from the _____________(south) part of China have been to Harbin twice.
3.As __________________ (travel), we should remember that when in Rome, do as Romans do.
4.Many visitors come to Xizang every year because of its ____________ (nature) environment.
5.Clean water is important to keep fish __________ (live) in the lake.
6.My hometown lies in the _________________ (northeast) part of our country.
7.The classmates became very ___________ (curiosity) about the tangram(七巧板) and wanted to have a try.
8.(2024湖南长沙中考改编)Our camp is ____________ (loca tion) in the Swiss Alps.
natural
　travellers/travelers
southern
　risky
　located
curious
　northeastern
　alive
综合训练
Ⅱ.阅读还原
根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
　　Rainforests are forests that get a lot of rain. It can rain more than one inch(=2.54 cm) per
day! There are tropical(热带的) rainforests all over the world. 　1　 They are very warm.The
Amazon is in South America. It is the biggest rainforest in the world. More than half of the
rainforest is in Brazil. 　2　
Many plants and animals live in the Amazon. There are more kinds of plants and animals
there than anywhere else in the world. The biggest mix of plants and animals lives in the canopy. 　3　 The canopy keeps off most of the sunlight. The rainforest floor is very dark.
　4　 There are more than 400 different native tribes(土著部落)! Native people used to
stay in the rainforest. They found food and built homes there. They made medicine from plants.
Now they sometimes leave. They go to nearby towns to sell food. Still, they live in their own
ways.
Today, the Amazon is faced with the problem of deforestation. This means that too many
trees are cut down by humans and　5　 What can we do to protect the rainforest and the wildlife
there
综合训练
A.The canopy is a thick coat of trees.
B.They are found near the equator(赤道).
C.it brings harmful results to the wildlife in the Amazon.
D.it makes more space for the animals in the Amazon to live in.
E.They have found some wildlife near the equator.
F.The rest spreads across eight other countries.
G.People live in the Amazon too.
1.______ 2.______ 3.______ 4.______ 5.______
　C
　G
　A
　F
　B
综合训练
Ⅲ.阅读理解
【跨地理·蓝洞】(2025湖北武汉模拟)
A blue hole is a flooded sea cave (洞穴) with a hole that opens up at the land’s surface. These cave systems form in carbonate rock, often on islands. Far below sea level there are some of the hardest environments on Earth,
with no oxygen (氧) and no light. Yet these areas are filled with life forms that have got usedto such conditions.
Blue holes get their name from the color that some have when seen from the air. It is usually a reflection of the sky on the water. ______ Some have dark or muddy water.
Blue holes have several layers of water, chemicals and bacteria (细菌). The top layer of fresh water comes from rainfall, which acts like a cap on top of the layered mixture and keeps out oxygen from the air. The fresh water
covers a denser layer of salt water. Underneath ____ is a layer of poisonous hydrogen sulfide (有毒的硫化氢),
produced by bacteria living in the water. At the bottom is anoxic seawater—water that does not have any oxygen.
　★
综合训练
“Underwater caves are probably one of the least understood ecosystems on the planet,”
Kenny Broad, a scientist at the University of Miami in Florida, says. “One reason is that you 、still physically have to go there—you can’t send in a submarine (潜水艇) or any other machine.”
There are many safety rules that divers must follow to help ensure their survival. First,
divers must have training to swim in such caves. Those who explore an underwater cave for the
first time must use a thin rope called a guideline, which helps them to safely enter and exit
without getting lost. Besides, divers must bring several light sources and more than one set of
breathing equipment (设备) just in case. And they must pay careful attention to their air supply (供应).
综合训练
1.【新中考·细节多选题】According to the passage, blue holes ______.( )
① are sea caves far below sea level ② give off bright blue light③ have life forms but no oxygen
and light④ are found mostly on islands⑤ include three layers in all
A.①②⑤　　　　B.②③④ C.①③④
2.Which of the following can be put in______ ( )
A.Why are blue holes in the color of the sky B.But not all of these cave systems have blue surface
C.What life forms can be found there D.How can water in blue holes change color
3.The underlined word “this” in Para. 3 refers to “______”.( )
A.the top layer of fresh water B.anoxic seawater
C.the layer of salt water D.bacteria living in the water
4.Blue holes are little understood perhaps because ______.( )
A.few instruments can be used to explore these cavesB.divers cannot ensure their survival there
C.the caves are full of poisonous matter D.they have ever-changing conditions
5.When exploring blue holes, divers must ______.( )
A.bring one set of breathing equipment and a light source B.be careful with their air supply
C.have a thin rope as a guideline anytime D.swim as quickly as possible to save time
C
B
C
A
B
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