常见的有以下六种情况：一、假如主句是将来时或表示将来含义时,那么条件和时间状语从句多用一般现在时如： When I grow up, I will be a nurse and look after patients/ I want to be a nurse and look after patients
我长大后要当一名护士，照顾病人
二、假如主句是祈使句，那么从句通常要用一般现在时如：Don't laugh at me when I make a mistake
我犯错误的时候不要笑话我
三、假如主句是含有情态动词的一般现在时，根据需要从句多用一般现在时如：You should be quiet when you are in the reading room在阅览室时应保持宁静
四、 假如 if 的条件状语从句遇到变换间接和直接时 , 祈使句应用 not to
如; She said not to close the window常见的时间状语从句的连词有:as soon as,when,while ,as，until 等五、主将从现说的是在含有时间状语从句和条件状语从句的主从复合句中,假如主句的时态是一般将来时，那么从句要用一般现在时
例如：I will tell him about it when he comes
If it is fine tomorrow， we will go outing
六、假如主句的时态是过去将来时，那么从句要用一般过去时
例如:He said that he would have another try if he had the chance
I knew he could help me if he was free the next day
主要标志有：if 、unless 、until、 when 、as
