我手里关于 when 用法的资料全再这了. 一、 when 意为“当…时”,用作连词,引导时间状语从句,从句的谓语动词可以是延续的(此时相 当于 while),也可以是非延续性的.引导的时间状语从句通常用现在时表将来. I will write to my sister when I have finished the book.我读完这本书后便给姐姐写信. When he sees the photo,he can't help thinking of his childhood. 每当看到这张照片,他就不禁想起童年. 二、 when 引导时间状语时,若主从句主语一致或从句主语为 it 且从句谓语动词含 be 的形式,可省 略从句的主语及 be 部分. When (I was) walking on the street,I came across Mary.我在街上漫步时遇上了玛丽. He gave good practical advice when (he was) asked.他有求必应,给出了好的可行性建议. She would weep when (she was) alone.她孤独时便哭. When(you are) in trouble,you can ask her for help.有麻烦时,你可找她帮忙. We will do that only when ( it is) necessary.只有当有必要时我们才会那么做. 三、 when 用作连词,表突然发生某事,意为“就在这时/那时”(=at this/that time),常构成句型 be doing… when… 或be about to do…/be on the point of doing… when…. I was just coming along to see you when I ran into Tom.遇见汤姆时,我正在来看你的路上. He was about to go to bed when the telephone rang.他准备睡觉时电话铃响了. 四、 When 用作连词表过早发生某事,意为“还没(刚刚)…就”,可构成句型 hardly/scarcely… when….使用该句型时应注意两点:① 主句的谓语动词用过去完成时,从句谓语动词用过去 时.②