1) when 当……时：
Does it hurt when I press here?
They usually leave when the work is done.
They were having their dinner when he arrived.
2) while 当……时，一面……一面：
She cut her finger while she was cutting onions.
We Should strike while the iron is hot.
we can Iook for Maria while you eat.
3) as 在……时：
He waved as the train left the station.
As he talked on he got more and more excited.
They looked up as she walked toword them.
4) before 在……之前，不等……就：
I said good bye before I left.
Take the medicine before you go to bed.
He ran off before I could stop him.
5) since 从……后，从……以来：
She has been an artist since she was five.
She has had a baby since she got married.
It's just a week since we came here.
6) until (till)直到，到……才：
I stayed with her until she died.
Don't leave till l get back.
7) as soon as 一……就：
As soon as you finish the job let me know.
As soon as he got well, he went back to work.
8) once 一旦……就：
It won't be difficult once yon have got used to it.
he said that, I knew he was lying.