He is a very efficient secretary, ______none of his predecessors

He is a very efficient secretary, ______none of his predecessors was.
A、that
B、which
C、of which
D、for which
【正确答案】：B
【题目解析】：在非限制性关系从句中，无论先行词是表人的还是表物的，我们都用which作为主语补语或宾语补语。