2020湖南专升本网分享：英语语法之动词不定式的用法

不定式结构作主语
1、不定式前置
1)Derive[A]mineral resources from<B>sedimentary rock[C]is a[D]major modern industrial activity.
不定式结构作主语
2)in the matriculation for postgraduate in a short time is realy a hard nut.
[A]To make high scores<B>To make low goal[C]To the high scores[D]Make the low goals
2、上述形式一般情况不多见，作为考试的规范英语，如果不定式较长，显得头重脚轻,则可由代词“it”作形式主语(形式主语“it”不能由“that”或“this”等其他代词代替)，而将不定式放到后面。
It is really a hard nut to get high scores in the matriculation for postgraduate in a short time.
3)John admitted that it's always difficult.
[A]for him being on time<B>being on time for him
[C]for him to be on time[D]on time for him
4)It is difficult for me
[A]to be concentrating<B>while someone[C]is using[D]a vacuum cleaner.
3、不定式后置的情况不仅限于动词是系动词，也适用于其他动词
湖北专升本网
It took us a great deal of efforts to finish that task.
It made him extremely happy to get contact with his family in Taiwan since they separated more than 40 years ago.
4、不定式结构所表示的动作是谁做的，即不定式的逻辑主语，通常可以在特定的上下文中能看出，也可以通过带“for+名词短语”辨出
It is quite important for us to read good books during the period of general review(总复习)。
It is not difficult for those who study maths well to pass the exam.
5、在某些形容词(如careless,clever,considerate等)作表语时，不定式后可以加of来引导出其逻辑主语
It is very kind of you to help me./It is stupid of him to do such a silly thing.
间或也可用for+there to be表示(而且there后面的不定式只能是to be)。
It's a great pity for there to be much trouble in the company.