I was just about to leave the house __ the telephone rang.A,when B,as C,as soon as D,while

问题描述:

I was just about to leave the house __ the telephone rang.A,when B,as C,as soon as D,while
我怎么觉得都对啊.
意思好像都一样.
可是答案选择A.困惑,求详解.

这是固定搭配 be about to .when.