( ) We were walking along the river _____ it suddenly began to rain.A.as B.while C.when D.then
问题描述：
( ) We were walking along the river _____ it suddenly began to rain.A.as B.while C.when D.then
答
Cwhen引导的时间状语从句，主句用过去进行时，从句用一般过去时
答
C
doing sth when。。。。
正在做某事，突然。。。
固定句型
答
C
be doing when 正要干某事,突然.
B连接两个长动作,排除,D语意错误
A没有be doing as的结构
【俊狼猎英】