（一）时间状语从句
表示时间的状语从句可由when, as, while, whenever, after, before, till (until), since, once, as soon as (或the moment ), by the time, no sooner … than, hardly (scarcely) … when, every time等引导。
e.g. When I came into the office, the teachers were having a meeting.
He started as soon as he received the news.
Once you see him, you will never forget him.
No sooner had I gone to bed than I went to sleep.
