If we some measures, we might have prevented the environmental pollutionA. takeB. had tak

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A. take
(答案→)B. had taken
C. took
D. have taken
解析：考查虚拟语气。与过去事实相反时，从句用过去完成时，主句用情态动词+have done.句意：如果我们采取了一些措施，我们也许就可以阻止环境污染。