They didn’t know how the change had .
A. been taken place
B. happen
C. e about
D. broke out
网友回答
A. been taken place
B. happen
(答案→)C. e about
D. broke out
解析：考查动词短语用法。Take place没有被动语态。B项应该使用过去分词的形式；break out指战争，火灾的爆发；e about产生，发生，该短语没有被动语态。句意：他们不知道这个变化是如何产生的。故C正确。