题干
What were you doing when the rainstorm came? 当暴风雨来的时候你正在做什么？
点拨：____意为"当……时候"，后面通常接时间点，从句中谓语动词用短暂性动词。另外，while，意为"当……时候"， 后面只能接一段时间，不能接时间点，其引导的从句的动作或状态往往与主句的动作同时发生。
While we were walking home, it began to rain.＝ ____
答案(点此获取答案解析）
when,It began to rain while we were walking home.
