Iwasjustleavinghomeitbegantorain.A.whenB.whileC.asD.so我觉得A和C都对,可答案说是A,说一下这两者的区别?

Question

I was just leaving home _____ it began to rain.A.when B.while C.as D.so
我觉得A和C都对,可答案说是A,说一下这两者的区别?

Answer 1

选A.A、B、C都翻译成“当.时候”但这个题是有公式的,共三条：
I was just doing sth when +一般过去时 我正在做某事突然另一件是发生...
I had just done sth when +一般过去时 我刚做完一件事另一件事突然发生...
I was about doing sth when +一般过去时 我正要做某事另一件是突然发生...
when都是“突然”的意思