We should always keep ________ in mind ________ friendship should be based on equality．

We should always keep ________ in mind ________ friendship should be based on equality．

A.it; what

B.it; which

C.it; that

D.that; that

答案及解析： C

解析：

考查句子结构。it作形式宾语，that引导真正的宾语从句。