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
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D解析思路分析：根据句子结构分析可知，若在空格处填上A、C两项，则会出现句式混杂现象；B项说法不存在。故选D项来引导一个非限制性定语从句，既合语法又合句意。
点评：该题考查非限制性定语从句，难度偏难。解答定语从句类题目时，应从分析句子成分入手，根据从句所需来选择合适的引导词。