Question

when非谓语动词doing

非谓语动词有时候也有when after这样的介词在前面 有时候可以省略 比如
Seen from the top of the mountain,the lake looks beautiful.这句能不能在seen前面加上一个when 好像After doing his homework,he went to bed.能不能把after省略了 非谓语动词前面加when after这是介词还是连词 那非谓语动词前能加if吗

Answer 1

Seen from the top of the mountain,the lake looks beautiful.不能加when,After doing his homework,he went to bed可以去掉after.
第一句是非谓语的用法,see与逻辑主语the lake是被动关系,所以用seen,此句也可以改成when引导的时间状语从句,When you see from the top of the mountain,the lake looks beautiful.
第二句中的after是介词,去掉after之后,就是非谓语作状语,这个句子也可以改成After he did his homework,he went to bed.这里的after是连词,不能去掉.
非谓语使用的地方是没有连词的,所以如果有if或者其他连词,就决不能用非谓语.
例1：Given more time,I will be successful.
例2：Give more time,and I will be successful.