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(共19张PPT)
Unit 2 Healthy Lifestyle
Period 2
Learning about language
动词不定式作主语
Infinitives as the subject
Look at the following sentences and pay attention to the infinitives.
Observe and Discover
1 To change bad habits is never easy.
2 It took the surgeon (n.外科医生) three hours to finish my mother’s lung surgery (n. 外科手术).
subject 主语
句子结构分析：
It takes sb some time to do sth
= To do sth takes sb some time.
(It 为形式主语，真正的主语to do)
subject 主语
形式主语
3. To join the People’s Liberation (n. 解放) Army,
it is required for men to shave off (剃掉)
their beards(胡须).
正常语序：
To shave off beards is required for men to join the People’s Liberation Army.
subject 主语
subject 主语
目的状语
4 It was not polite to disturb(v. 打扰)your neighbours with loud music last night.
正常语序：
To disturb your neighbours with loud music last night was not polite.
It is +adj (for sb) to do sth
subject 主语
subject 主语
It
is never easy
to change bad habits.
Tip 1：将形式主语 ______ 置于句首，____________ 置于句末，可以
避免句子头重脚轻、结构失衡。
Change the sentence structures.
it
动词不定式
Tip 2: 动词不定式作主语时，谓语动词常用__________。
To change bad habits is never easy.
To help others gives a person satisfaction（满足）.
To prevent harmful habits like these from dominating a teenager’s life is essential.
Task 2: Observe and explore.
单数
Tip 3: 在 It + is/was + 形容词 + to do 的句式中, 当该形容词用以表示to do的特征时，使用 It is/was ＋ adj. ＋ ____ + sb. + to do；当该形容词用来表示不定式的逻辑主语(sb.)的性质、特征或品德时，使用 It is/was ＋ adj. ＋ ____ + sb. + to do。
for
of
1. It isn’t right for us to stop half way. = To stop half way is not right.
2. It’s kind of you to think so much of us. = You are kind to think so much of us.
It is +adj.+ for/of sb. to do sth.
1) It is ＋ adj. ＋for sb. to do sth.
此处的形容词用来修饰后面的动词不定式，
常用于表示事物的特征，用于此句型的形容词有：easy, hard, difficult, possible, important, impossible,
necessary, good, bad, exciting, interesting, surprising等。
It is necessary for young students to learn a foreign language.
对年轻的学生来说，学习一门外语是必要的。
As we all know，it is good for you to keep exercising.
众所周知，坚持锻炼益于健康。
2) It is ＋ adj. ＋of sb. to do sth.
此处的形容词用来修饰sb，常用于表示事物的特征，用于此句型的形容词有：kind, nice,wise, silly, polite, impolite, friendly,
foolish, clever等。
It was careless of him to make such a mistake.
出了这样的错误，他太粗心了。
It’s very kind of you to say so.
你这样说真是太好了。
It was rude of the boy to speak loudly in public!
那个男孩在公共场合大声说话真是太无礼了!
Tip 4: 动词不定式也可用在 it+be+n.+to do sth的句型结构中，it 做 __________ ，正真的主语是_____________ 。
Observe and Discover
1. It’s our duty to do that.
2. It’s a mistake not to help them.
3. It must be great fun to fly to the moon in a spaceship.
动词不定式
形式主语
Tip 5: 动词不定式充当 ，用在表示某人花多少钱或金钱做某事的句型：_______________________________________ 。
1. It took me more than an hour to do my homework yesterday evening.
2. It will take us a long time to walk there.
3. How long does it take to get there
4. How much did it cost you to send the package
It takes (costs) sb some time / money to do sth
Observe and Discover
主语
Observe and Discover
1. ________ to handle the rubbish is the question.
2. ________ to go for dinnerhas not been decided.
subject 主语
How
Where
subject 主语
Tip 6:________ 和动词不定式构成不定式短语作主语。疑问词包括疑问代词who、whom、what、which、whose以及疑问副词when、where和how。此外连接词whether也适用。
疑问词
1.It took us about two hours (get) there that day.
2.Whether (hold) a party this weekend hasn’t been known yet.
3.It is foolish you to take a taxi to the town in that situation.
4.It is important for her (prepare) for the examination.
5.It’s our duty (keep) our environment clean and tidy.
6.It is no good for you (wait) here for a long time.
7. (get) there by bike will take us half an hour.
to get
to hold
of
to prepare
to keep
to wait
To get
Exercises
动名词作主语表示_______________ 的行为;不定式作主语表示 _____________________________ 动作。
Further thinking
1. ______ (do) morning exercises regularly is good for your health.
2. It feels really good ______ (do) morning exercises today.
Doing
to do
经常性或习惯性
具体的、一次性的或将来的
Complete the following sentences and compare their usages.
Conclusion
Summary
1.to do作主语，表具体的特指未完成动作,谓语用单数（doing作主语常表习惯性动作）
To change bad habits is never easy.
2.it作形式主语常见于以下情况中(真正的主语—不定式)。
1) It is + adj. + for（表事物特征）/of（表品质） sb. to do sth.
表品德的adj:kind, nice, wise, silly等
表事物特征的adj: easy, hard, difficult, possible
2( It is + n. + (for sb.) to do sth. 常见的名词有：pity, shame, pleasure
3)It takes/took/will take sb. some time/money to do sth.
3.疑问词who, whom, whose, what, which, when, where, how+to do，也可作主语。
Thank you!

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