__he was crossing the bridge,the earth suddenly began to shake.a)wgile b)when c)as d) after
问题描述：
__he was crossing the bridge,the earth suddenly began to shake.a)wgile b)when c)as d) after
答
A
四个选项中 其实when as while 这三个词都对 .都表示表示一个动作的发生时 另外一个动作的发生
但是在选择题中当然不能多选、而as 和when在引导时间状语从句时几乎可以对等、所以按排除法就只能选A while