(课件网) Discovering Useful Structures—Infinitives(3) as the subject Unit 2 Healthy lifestyle 语境 感悟 阅读以下短文，感知加颜色句子，并完成下面的练习 I had a lot of hobbies when I studied in college.①It was hard for me to save money to keep my hobbies.②It was foolish of me to spend plenty of time with those.③But to study hard was my first task at that time.I often got up early to catch up with other students.④It took me two terms to make up for my lost time.⑤I think to make the same mistake is not wise because to become a surgeon is not easy.I should seize the good opportunity and do whatever I can to achieve my ambition.Now，I am a doctor and I will never forget the experience of that time. 【自主发现】 1.以上加颜色句子中动词不定式都作 。 2.句①、句②和句④中it作 ，真正的主语是后面的_____ 。 主语 返 回 形式主语 动词不 定式 语法 精讲 一、基本用法 1.动词不定式作主语时，谓语动词用单数。 To look after these naughty boys is really difficult. 照看这些淘气的男孩真的很难。 To love and to be loved is the greatest happiness one can get. 爱与被爱是一个人能获得的最大幸福。 2.为了避免头重脚轻，常用it作形式主语放在句首，作主语的不定式常置于句末。 It’s necessary for you to lock the car when you do not use it. 当你不用汽车的时候，锁车是有必要的。 It’s nice for you to go there. 你还是去那里的好。 注意： 1.若要说明不定式表示的动作的发出者，就要在不定式前加for引起的短语，构成“for＋名词(或代词宾格)＋不定式”短语，这一短语被称为不定式的复合结构。 2.在“It is＋adj.＋不定式复合结构”句型中，当其中的形容词是说明逻辑主语的性质、品质时，要由of引出逻辑主语，不能用for。这类形容词主要有clever，foolish，kind，nice，careless，polite，silly，stupid，wise等。 It’s very easy for him to work out this math problem. 对他来说解出这道数学题很容易。 It was careless of him to make such a mistake. ＝He was careless to make such a mistake. 犯了这样的错误，他太粗心了。 二、动词不定式和动名词作主语的异同点 1.不定式和动名词作主语的相同点 (1)不定式和动名词作主语时，常常为了保持句子的平衡，用it来作形式主语，如： It is not easy to learn English well. 学好英语不容易。 It is no use asking him for help. 向他求助是没有用的。 (2)如果主语用了不定式，表语和宾语也要用不定式；如果主语用了动名词，表语和宾语也要用动名词，这在英语中称为对称性，如： To see is to believe.＝Seeing is believing. 眼见为实。 It is better to stay home than to go out. 待在家里比出去要好。 2.动名词和不定式作主语的不同点 (1)不定式作主语常表示具体的某一动作；表示泛指或一般的抽象的概念时，多用动名词。 To visit China with my teammates is my next goal. 和我的队友一起去中国旅游是我的下一个目标。 Walking is a good form of exercise for both the young and the old. 散步是一种老少皆宜的很好的运动方式。 (2)在“It＋be＋no use(good/help/need等)”之后常用动名词作主语，而少用不定式。 It is no use crying over the spilt milk. 覆水难收。 It is no help taking this medicine. 服用这种药没有用。 注意：如果该句型中用了for引出不定式的逻辑主语，就只能用不定式。 It is no good for us to do th ... ...
