I doubt ___ David told us the truth,but they never doubt ___ David is honest

题目

I doubt ___ David told us the truth,but they never doubt ___ David is honest
A if;if
B if;that
C that;that
D that;if

答案

B
我怀疑戴维是否告诉我们真相,但是他们从不怀疑是否诚实.