1、不定式作主语【观察例句】1To say is one thing and to do is another. 2Its rude to turn your back to your teacher and refuse to answer.3It is impossible to learn a foreign language without making painstaking effort.4It seemed a pity to have wasted so much time.【归纳用法】1把不定式置于句首。如：To get there by bike will take us ha
2、lf an hour.骑自行车到那儿将花费我们半个小时。To make a plan first is a good idea.首先制定好计划是个好主意。2用it作形式主语，把真正的主语不定式置于句后，常用于下列句式中。如：(1)Itbe名词to doIts our duty to take good care of the old.照顾好老人是我们的责任。(2)It takes sb.some timeto doHow long did it take you to finish the work?你花了多少时间来完成这项工作？(3)Itbe形容词for sb.to doIt is diff
3、icult for us to finish writing the composition in a quarter of an hour.我们难以在15分钟内完成这篇作文。(4)It seems(appears)形容词to doIt seemed impossible to save money.省钱似乎不可能。(5)It 不定式结构可位于believe/consider/discover/expect/find/think和wonder之后He thought it would be safer to go by train.他认为乘火车比较安全。(6)不定式的完成式也可作句子的主语To
4、 have made the same mistake twice was unforgivable.犯同样的错误两次是不可原谅的。It is better to have loved and lost than never to have loved at all.爱过之后失去了爱，比从未爱过要好。即学即练1单句语法填空To make(make) up for lost time is not possible.It is good for your study to discuss(discuss) with your classmates.3不定式和动名词作主语的区别(1)动名词作主语通
5、常表示抽象动作；而不定式作主语表示具体动作。Smoking is prohibited here.这里禁止抽烟。(抽象)It is not very good for you to smoke so much.你抽这么多烟对你身体很不好。(具体)(2)动名词作主语时，通常用以表示一件已知的事或经验；不定式短语通常用来表示一件未完成的事或目的。Climbing mountains is interesting.爬山很有趣。(经验)To finish the task will take a long time.要完成这项任务将要花费很长时间。(具体)即学即练2单句语法填空Watching(wat
6、ch) news on TV has become a routine for me.It took me only five minutes to finish(finish) the job.单句语法填空1To lean(lean) out of the window is dangerous. 2To save(save) money now seems impossible. 3It is an offence to drop(drop) litter in the street. 4It is stupid of you to write(write) down everything
7、 (that) the teacher says. 5Driving(drive) a car during the rush hour is tiring. .短文语法填空I have a lot of hobbies 1.when I studied in college. It was hard for me to save money 2.to keep(keep) my hobbies. It was foolish of me 3.to spend(spend) plenty of time with those.But 4.to study(study) hard was my
8、first task at that time. I often got up early 5.to catch(catch) up with other students. It took me two terms 6.to make(make) up for my lost time. I think 7.to make(make) the same mistake is not wise because 8.to become(become) a surgeon is not easy. I should take hold of the good chance and spare no effort 9.to achieve(achieve) my goal. Now，Im a doctor，10.and I will never forget the experience in that time.
