题目内容：

he asked nothing because he was able to understand what they had talked about.
He asked nothing because he was able to understand what they had talked about.
A.must B.was able to C.can D.may

优质解答

be able to 是能够做某事,must是必须,
这里是过去时态,所以不能用can和may
结合语境应该是选B