连词: when, whenever, before, after, while, as, once (一旦)，until, (ever) since, as soon as等。
eg: When you cross a road, you must be careful.
It will not be long before we meet again.
She comes here every month since she was a child to see her grandmother.
As soon as I know it, I'll tell you.
eg: Sit down wherever you like.
Put it where you found it.
连词: if, unless, as/so long as (只要)，in case(万一)等。
eg:As/So long as we don't give up, we are bound to succeed.
In case I gorget, please remind me of that.
If it snows tomorrow, we will stay at home.
I will do anything as long as it is interesting.
连词: because,as (由于，因为)，since (由于，既然)，now that (既然)，that,等。
eg: As I didn't know the way, I asked a policeman.
Since no one is against, we'll adopt the proposal.
Seeing that she's ill, she's unlikely to come.
I’m glad that you’ve come.
Now that the kids have left home,we’ve got a lot of extra space.