While we were sleeping, it snowed! It snowed while we were sleeping! While he was cooking, a parcel arrived. A parcel arrived while he was cooking. 2 “While” 作连词时，可以表示 “但是，然而”。 One of the twins is shy ...

“When、as” 和 “while” 在日常生活中和书面写作当中的使用频率非常高。 它们都可以引导时间状语从句，用来说明一句话中两个动作发生的时间点。 接下来，我们就通过对比时间状语从句中，主句与从句的时间关系，来讲解 “when、as、while” 的用法和区别。