It began to snow ____(when while)the man was walking down the stree.说原因~·
问题描述：
It began to snow ____(when while)the man was walking down the stree.
说原因~·
答
实际上when，while的function差不多，while更倾向于连接同时发生的两个动作，做题的话while更好一点。但是这种题目没什么意义，native speakers 在说话的时候不会故意区分这两个词
答
while
书上这种句式很多
.did .while .was doing
was doing.when .did