Everyone says I must be mad and they are probably right.________they are.

问题描述:

Everyone says I must be mad and they are probably right.________they are.
(a) Of course (b) It's certain (c) Perhaps (d)It's sure

C
A of course 不能引导句子
B It's certain that 加句子,少了that不行
D 和上面道理一样,少了that