w h e n-d o i n g-的用法
When + doing"的用法
Every teacher should, therefore, follow in his footsteps and emphasize benevolence when teaching.
因此，每个老师教学时，应效法孔子并强调仁的道理。

= Every teacher should,therefore,follow in his footsteps and emphasize benevolence when he teaches .
在以when,while,if, once ,though,unless 等六个连词引导的状语从句中，若主语与主句的主语相同时，可将从句中的主语删除，并将之后的动词变成现在分词。

若是be动词，一律变成分词being,而being再予以省略。

1. when you do the work, you should be careful.
= When doing the work, you should be careful.
2. If I am free, I'll do it.
= If free, I'll do it.
3. when you do the work, you must be careful.
= When doing the work, you must be careful.
4. Though he is poor, he is happy.
= Though poor, he is happy.
5. While I was watching Tv, I fell asleep.
= While watching TV. I fell asleep.
6. When you drive a car, you should be alert.
= When driving a car, you should be alert.。