It is reported that two schools,________ are being built in my hometown,will open next year.

问题描述:

It is reported that two schools,________ are being built in my hometown,will open next year.
A.they both B.which both C.both of them D.both of which
C ,我觉得应该是 D,到底是什么呢

答案肯定错了,不可能是C,两个句子之间必须有连词连接
答案就应该是D