when: Don't get excited when you talk. 讲话时别激动。

　　while: We must strike while the iron is hot. 我们要趁热打铁。

　　as: He smiled as he passed. 他经过时笑了笑。

　　before: It will be five years before we meet again. 要五年后咱们才能再相见。

　　since: How long is it since you came to London? 你到伦敦有多久了?

　　whenever: Whenever it is possible, they play outside. 一有机会他们就到外面玩耍。

　　after: I'll tell them after you leave. 我将在你走后告诉他们。

　　until, till: I propose waiting till the police get here. 我建议等警察来了再说。