Personally I think it is the sales manager rather than the salesgirls to blame.---

问题补充：

--- Personally, I think it is the sales manager, rather than the salesgirls, to blame.

--- I can’t agree any more.

A. is

B. that is

C. are

D. who are

答案：

A. is

(答案→)B. that is

C. are

D. who are

解析：通过分析句子结构，可知这个句子中包含一个强调句型。因为去掉it is和that，剩下的是一个完整的句子，所以是强调句型，强调句的结构It is/was+被强调部分+that+句子的其他成分。