● 例如:It is necessary (for you) to give up smoking. = (For you) to give up smoking is necessary.
对于你来说,戒烟是十分必要的。
不定式一般式to give up smoking做主语,表示将来,for you做不定式的逻辑主语,在听者清楚动作执行者的情况下,for you 也可省去。为了保持句子平衡,一般用it做形式主语,不定式短语往往放在表语之后, 做真正主语。
本句用复合句形式为:It is necessary that you should give up smoking.
● To protect the environment is everyone’s duty.= It is everyone’s duty to protect the environment. 保护环境人人有责。
不定式一般式to protect the environment用来表示警句。
●Teaching is a tiring but satisfying job.
教书是十分辛苦然而却令人感到满意的职业。
动名词"Teaching” 担当主语,表示概念。
● It is no use asking me. I know no more than you know.
你问我根本没用,我还没你了解得多呢。