Had they known what was ing next, they second thoughts.
A. may have
B. could have
C. must have had
D. might have had
网友回答
A. may have
B. could have
C. must have had
(答案→)D. might have had
解析：考查虚拟语气：若与过去事实相反，虚拟语气的条件从句的谓语用过去完成时(had+过去分词)，可以把had提到主语前，构成倒装句，主句谓语用“should (would, could, might)+have+过去分词”。句意：要是他们知道下面会发生什么，就会再好好想一想了。选D。