【题目】Maria has written two novels, both of ________ have been made into television series.
A.them
B.that
C.which
D.what

【答案】C
【解析】句意：Maria已经写了两部小说，它们都被制作成了电视剧。句中有逗号，说明是非限制性定语从句，them不能引导定语从句，that不用于非限制性定语从句和介词之后，what不用于定语从句，排除A、B、D；both of which相当于and both of them，故选C。