四、非谓语动词形式的判断

    (一)通常要考虑两大因素：时间因素、语态因素。见下表：

    在作定语、宾语补足语时，表示过去已经发生的被动语态.一般用过去分词而不用having been done。

    (二)充当句子各成分的非谓语动词辨析

    1.作主语：动名词作主语表示一般性的动作。不定式作主语表示具体的、特别是将来的动作。如：

    Walking is a good form of exercise forboth young and old.

    To be an actor is his dream.

    2.作表语：

    (1)动词不定式和动名词作表语说明主语的内容，可以与主语交换位置，其区别同作主语时的区别一样。如：

    His job is building houses=Buildinghouses is his job.

    Our task now is to increase fbod production=To increase fnod production is our tasknow.

    注意.be to do有时可作为一种谓语结构 ......