题目内容
【题目】I was about to go to bed ________ there was a knock at the door.
A. while B. when C. as D. suddenly
【答案】B
【解析】
试题分析：考查固定用法。sb be about to do sth when sth happen.某人正要做某事突然（就在那时）另一件事情发生了。此处的when相当于 at that time，不能用while代替。故选B
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