___ he was on holiday he caught a cold.A.When B.While C.As D.At
问题描述：
___ he was on holiday he caught a cold.A.When B.While C.As D.At
答
When后可接时间点和时间段,while后只能接时间段,不能接时间点,as表示进展过程,有一边一边的意思,at是指在某个时间点.所以选B