1. 用作主语直接把动词不定式置于句首的状况不多，多数状况用it作形式主语，把真的的主语动词不定式置于句末，尤其是不定式短语较长时。动词不定式作主语，谓语动词用第三人称单数形式。带疑问词的不定式短语作主语常置于句首。It is our duty to try our best to deal with these problems.尽最大努力处置这类问题是大家的责任。The head teacher said it was necessary to talk with his mother.校长说，和他母亲谈一谈非常有必要。How to learn English well is important.怎么样学好英语非常重要。Tosee is to believe.眼见为实；百闻不如一见。
