几个英语题,帮忙回答下,详细些

几个英语题,帮忙回答下,详细些
1.-Are you going o Guilin by plane?
-It's fast but expensive, so I'm not sure.I 什么 take a train.
A.should B.may C.must D.will
这个我看哪个都可以啊
2.Joe has been studying Chinese for three months,but he can 什么 understand people when they speak Chinese.
A.nearly B.certainly C.usually D.hardly
这题凭什么就选D呢?
3.-Do you mind if I sit here?
-什么.It's for Miss Wood.
A.Not at all B.Never mind
C.You'd better not D.Of course not
为什么不选D
4.The book 什么 from the library must be returned this afternoon.
A.which you borrowed it
B.why you borrowed
C.you borrowed
D.what you borrowed
为什么不选A