They were waiting for the bus when it started to rain.

开始下雨时他们正在等公交车。

同一单元的其他句子

• I was reading a book when the rainstorm came.暴风雨来的时候我正在看书。
• What were you doing when the rainstorm started?暴风雨开始时你在做什么？
• She was cooking dinner while it was raining heavily.下大雨的时候她正在做晚饭。
• They were playing basketball when the storm hit.暴风雨来袭时他们正在打篮球。
• He was sleeping when the thunder woke him up.雷声把他吵醒时他正在睡觉。