一、引导词的选择：
1.时间状语从句
1).由when 、 while、as（当……时候）引导的时间状语从句。
When jack got home , his mother was cooking .
2).由after/ before (在….之后/ 前)引导的时间状语从句。
The football match played after school was over .
3).由as soon as (一…..就……)引导的时间状语从句。
I’ll ring you as soon as I reach Beijing .
