【题目】______ scientists have learned a lot about the universe, there is much we still don't know.
A.Once
B.Since
C.Though
D.Unless

----_______.

A. That’s a good point B. With pleasure C. It’s my pleasure D. Very much

【题目】— Can you come to a party on Saturday, Peter?
— Oh, ______I'm already going out, I'm afraid.
A.what a pity!
B.don't ask!
C.how come?
D.so what?

【题目】That's why I help brighten people's days. If you ________， who's to say that another person will?
A.didn't
B.don't
C.weren't
D.haven't