1) because 因为：
I study English because it is useful for my work.
She is in bed beouse she is ill.
Because they lived on the edge of the Persian Empire, they were ruled by the king of Persia .
2) as 因为，由于：
As he wasn't ready he didn't come with us.
We couldn't go to school as life was very hard then.
As you can't drive, you must go by bus.
3) since 既然，由于：
Since you don't want to go, we won't force you to.
We had to put the meeting off since so many people were absent.
Yon may take this book since I have read it.
4) now (that)既然已经：
Now that you are all back, we'd better start the work right away.
Now(that) you are well again, you can travel.
My mother runs it now that she and Dad are divorced.
5) seeing that 由于，考虑到：
Seeing that nobody was very enthusiastic about it, they decided to cancel the trip.
He has done well to pass his exams, seeing that he has been ill a lot.