不定式的复合结构:for...to do sth 不定式的逻辑主语明确是谁时,是不用复合结构的,即:to do sth ;否则,用复合结构. 不定式的句法作用举例如下: 1.主语:It is very important for you to study English. 2.表语:The car is for you to drive. 3.状语:The man works hard for his boss to be pleased. 4.定语:There is no need for you to go to the office. 5.宾语:I've arranged for her to see you off.