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八年级下册英语Unit4阅读限时练
一、完型填空。（限时8分钟）
The Deep Ocean: A Mysterious World
The ocean covers about 71% of Earth's surface, but we have explored 1 5% of it. The deep ocean is the largest living space on our planet, yet it is one of the least understood. The 2 point is the Mariana Trench, which is nearly 11 kilometers deep. The pressure there is over 1,000 times 3 than at sea level.
Sunlight can only reach about 200 meters below the surface. Below that, it is completely dark. 4 , many amazing creatures live in the darkness. Some make their own light through bioluminescence(生物发光). The anglerfish, for example, has a part on its head that glows to 5 prey.
Scientists explore the deep ocean using special submarines and robots. These machines are very expensive and can 6 for months. In 2012, film director James Cameron went down to the Mariana Trench in a submarine called Deep-sea Challenger. He spent about three hours at the bottom, 7 samples and taking photos.
The deep ocean is also important for our future. It has rare minerals that we use in computers and phones. Some sea creatures might have chemicals that can help make new 8 . However, we must be careful. The deep ocean is very fragile(脆弱). If we damage it, it might never recover. Pollution and deep-sea mining are becoming 9 threats(威胁).
We need to protect this mysterious world. As we learn 10 about the deep ocean, we realize how much we still have to discover. It is a frontier as exciting as outer space, and it is right here on our own planet.
( )1. A. less than B. more than C. exactly D. almost
( )2. A. deepest B. highest C. coldest D. hottest
( )3. A. higher B. lower C. stronger D. weaker
( )4. A. However B. Therefore C. Because D. Although
( )5. A. avoid B. attract C. feed D. hide
( )6. A. cost B. take C. spend D. pay
( )7. A. buying B. selling C. collecting D. making
( )8. A. food B. clothes C. medicine D. buildings
( )9. A. smaller B. bigger C. fewer D. less
( )10. A. fewer B. less C. more D. many
二、阅读理解。（限时15分钟）
A
The Sahara Desert is the largest hot desert in the world. It covers about 9,200,000 square kilometers in North Africa. How do you read that number It is “nine million two hundred thousand square kilometers”. That is much larger than the United States.
The Sahara is also one of the driest and hottest places on Earth. In summer, the temperature can reach over 50°C. That is hotter than most other places. However, at night, it can become very cold — sometimes even below 0°C. So the Sahara has a bigger temperature difference between day and night than many other deserts.
On the other hand, the Dead Sea is not a sea — it is a salt lake. It is the lowest point on Earth’s land, at about 430 meters below sea level (read: four hundred thirty meters). The water in the Dead Sea is much saltier than ocean water. In fact, it is the saltiest body of water in the world. Because of that, people can float easily without swimming.
Although the Sahara is the largest hot desert, the coldest desert on Earth is Antarctica. Antarctica is even larger than the Sahara, but it is much colder. The lowest temperature ever recorded there was -89.2°C (minus eighty-nine point two degrees Celsius).
So when we talk about “the most” or “the largest”, different places hold different records. Geography is full of amazing numbers and comparisons.
( )1. How large is the Sahara Desert
A. 9.2 million square kilometers.
B. 9.2 thousand square kilometers.
C. 92 million square kilometers.
D. 920 thousand square kilometers.
( )2. The temperature difference in the Sahara between day and night is ______ that of many other deserts.
A. smaller than B. bigger than C. the same as D. less than
( )3. Why can people float easily in the Dead Sea
A. Because it is very deep.
B. Because the water is warm.
C. Because it is the lowest place.
D. Because the water is very salty.
( )4. Which desert is larger, the Sahara or Antarctica
A. The Sahara. B. Antarctica.
C. They are the same size. D. It is not mentioned.
( )5. What does the writer want to show in the last paragraph
A. The Sahara is the best desert.
B. The Dead Sea is not a real sea.
C. Different places have different “most” records.
D. Antarctica is too cold for people.
B
Extreme Numbers in Nature
Nature is full of amazingly large numbers. Let's look at some examples.
First, consider the Amazon Rainforest. It produces more than 20% of the world's oxygen(氧气), which is a much larger percentage than any other forest. The number of tree species in the Amazon is estimated to be around 16,000, and the number of individual trees is approximately (大约) 390 billion. That's 390,000,000,000 trees!
Next, think about the Sahara Desert. It is the largest hot desert in the world, covering about 9,200,000 square kilometers. That's almost the same size as China! Surprisingly, the Sahara wasn't always a desert. About 10,000 years ago, it was much greener and wetter, with many lakes and rivers.
Now look at the world's oceans. They contain about 1,332,000,000 cubic kilometers of water. If all this water were spread evenly over Earth's surface, it would cover the planet to a depth of more than 2,600 meters. The longest mountain range on Earth is actually underwater—the Mid-Ocean Ridge stretches for about 65,000 kilometers, which is longer than the circumference(周长) of Earth!
Finally, consider the atmosphere. Every square centimeter of your skin has about 1 kilogram of air pressing on it right now. The total weight of the atmosphere(大气) is about 5,148,000,000,000,000 kilograms. That's 5.148 quadrillion(千万亿) kilograms!
These huge numbers help us understand how amazing and powerful nature really is.
( )6. What percentage of the world's oxygen does the Amazon Rainforest produce
A.More than 20%. B.More than 10%.
C. More than 30%. D. More than 50%.
( )7. How many individual trees are there in the Amazon Rainforest according to the passage
A.About 16,000. B. About 390 million.
C. About 390 billion. D. About 5.148 quadrillion.
( )8. What was the Sahara Desert like about 10,000 years ago
A.It was larger than it is now.
B. It was smaller than it is now.
C. It was exactly the same as now.
D. It was much greener and wetter.
( )9. How long is the Mid-Ocean Ridge
A.About 2,600 meters. B. About 9.2 million kilometers.
C. About 65,000 kilometers. D. About 1.332 billion kilometers.
( )10. What is the main idea of this passage
A.The Amazon Rainforest is important.
B. Nature contains many extreme and large numbers.
C. The Sahara Desert is the largest desert.
D. Numbers are boring and difficult to understand.
三、阅读下面短文，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。（限时7分钟）
The Mariana Trench is the deepest place on Earth. It is located in the Pacific Ocean. 1. .That number is “eleven thousand thirty-four meters”. To understand how deep it is, think about Mount Qomolangma. It is about 8,849 meters high. 2. . That means the trench is much deeper than the mountain is high.
The pressure at the bottom of the trench is very high — more than 1,000 times the pressure at sea level. 3. . In fact, the temperature there is just a few degrees above freezing.
Only a few people have ever reached the bottom of the Mariana Trench. The first were Don Walsh and Jacques Piccard in 1960. 4. . That is much deeper than the deepest part of the Dead Sea (about 430 meters below sea level).
The Mariana Trench is not only the deepest but also one of the least explored places on Earth. 5. .Every time scientists go there, they discover new species (物种). That makes it one of the most exciting places for ocean research.
A. It is also very cold and dark down there.
B. The temperature there is higher than that on the land.
C. Its deepest point is about 11,034 meters.
D. If you put Mount Qomolangma into the trench, its top would still be over 2,000 meters underwater.
E. Many tourists visit the Mariana Trench every year.
F. That is even deeper than Mount Qomolangma is high.
G. Scientists know less about it than they know about the surface of Mars.
四、短文填空。（限时8分钟）
China, run, in, because, ton,develop, city, feed, clear, old
The Yellow River runs from the mountains to the sea. It gave birth to one of the 1. and most famous cultures in the world-the Yellow River culture. In the hearts of 2. people, the Yellow River is the "mother river". It plays a more important role in our country's 3. .
The river got its name Huanghe in Chinese4. its water is yellow, as it took lots of yellow sand to the water when it ran through the Loess Plateau (黄土高原).
The river starts from Qinghai Province5. the northwestern part of China. It runs through a lot of places before 6. into the Bohai Sea. The 5,464-kilometre-long river 7. about 12% of China's population and provides(提供) water for about 15% of fields and more than 60 8. .
Our country has made great efforts(努力)in the environmental protection of the river these years. Each year over 400 million 9. of sand is stopped from being washed into it. Our mother river gets much 10. than before.
参考答案
一、1-5 AACAB 6-10 ACCBC
二、1-5 ABDBC 6-10 ACDCB
三、1-5 CDAFG
四、1. oldest 2. Chinese 3. development 4.because 5. in 6. running 7. feeds 8. cities 9.tons 10.clearer
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