问题
选择题
We were about to go out for a walk ______ it began to rain.
A．while
B．before
C．as
D．when
答案
D
题目分析：考查固定句式。固定句式：be about to do sth when…正要做某事在这时…。本题中的when是一个并列连词，意为：在那时；故D正确。
点评：固定句式：be about to do sth when…正要做某事在这时…。本题中的when是一个并列连词，意为：在那时；对于这样的固定句式，平时要加强识记。