1．when，while，as
三者均可译为“在……时候”。when引导的从句，动词既可以是延续性的，也可以是终止性的。一般来说，当主句的动作正在进行时，when引导的从句的动作才发生；while引导的从句中，动词只能是延续性的，一般来说，当while引导的从句的动作正在进行时，主句的动作才发生；as表示随着短暂动作的发生，另一行为伴随发生。
He was riding to school when he was hit by a car this morning.
当他被一辆小汽车撞到的时候他正骑车上学。
You'd better turn off the water while you brush your teeth.
当你刷牙的时候你最好关掉水。
She sang as she walked. 她一边走一边唱歌。
2．so…that…，such…that…
so＋形容词＋a/an＋可数名词的单数＋that从句；
so＋many/much/few/little＋名词＋that从句；
such＋a/an＋形容词＋可数名词单数＋that从句；
such＋形容词＋不可数名词/可数名词复数＋that从句。
Hangzhou is so beautiful a city that lots of visitors come here every year.
杭州如此美以至于每年许多游客来这。
She is such a good girl that we all like her.
她是如此好的一个女孩，以至于我们大家都喜欢她。
There are so many students on the playground.
操场上有如此多的学生。
