同学你好，该知识点来自沪江网校《【Uni智能】雅思7分一站式VIP-大学起点【全额奖学金签约班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好
动词按其动作发生的方式、动作发生过程的长短，可分为延续性动词和终止性动词。


延续性动词

表示能够延续的动作。如：study, work, stand, lie, know, walk, keep, have, wait, watch, sing, read, sleep, live, stay等。延续性动词可以与表示时间段的状语连用。
表示时间段的短语有:for+ 时间,for 2 years; since从句,since he came here; since+时间点名词,since last year, since 5 days ago; how long; for a long time等。
例:He has lived here for 6 years. You can keep the book for 5 days. I stayed there for 2 weeks last year. How long did you stay there last year?


终止性动词

也称非延续性动词、瞬间动词或点动词，表示不能延续的动作,这种动作发生后立即结束。 如:open, die, close, begin, finish, come, go, move, borrow, lend, buy,arrive等。
非延续性动词在肯定句中与表示时间点的状语连用，如：two years ago; at 5 o'clock;
例:He died 5 years ago.
否定的终止性动词可以与表示时间段的时间状语连用。例:I haven't left here for 3 years. I haven't heard from him for 3 weeks.

所以when这些动词都是可以引导的