求助一道语法题！！！

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While recognizing that lying oftenfacilitates social interactions, psychiatrists are seeking to determine when theybecome destructive and which kinds of mental problems they can signal.

   A.    they become destructive and which kinds ofmental problems they can signal

   B.    they become destructive and the mentalproblems that are signaled by them

   C.    it becomes destructive and what are thekinds of mental problems they signal

   D.   it becomes destructive and the mentalproblems that are signaled by it

   E.    it becomes destructive and which kinds ofmental problems it can signal
这道题目正确答案选择E，我选择了A。因为我无法理解it指代哪个啊！！！！。。。。。求大神给我讲解一下这题it指代什么，以及原因，谢谢了！！！