1.I was doing my homework ______ my mother came in .
A, while B. when C. as soon as D. as long as
2. ______ they are waiting for the New Year , they listen to the music,sing songs and have fun .
A. while B. until C. when D. as soon as
3. We are cleaning the room ______ they are watching TV .
A. When B. while C. as soon as D. before
When : 当----时候， 可表示瞬间、时间段，与主句所叙述的动作可
While : 连接时间状语时，表示主句的行为在从句行为过程中发生，
1. It has been 3 years ______ I came to Run’an School .
A. as soon as B. until C. while D. since
2. I have been in this school ______ I came to Hefei 9 years ago .
A. since B. after C. until D. when
3. It is 20 years since I _______ to teach English .
A. begin C have begun C. began D. will begin
4. -----How long have you benn here ?
------ _____ 2001.
A. in B. for C. since D. after
Since ：引导的时间状语从句， 表示“自----以来”主句用一般现在时或
it has been ----since 从句 或 it is ------since从句
在现在完成时中，注意和 for 进行区别。