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：句意：如果他们知道接下来是什么,他们可能会重新考虑的。Had they known what was ing next=If they had known what was ing next，表示如果过去他们知道将会发生什么事，后半句应用 could/should /might/would+have+p.p.的形式，表示对过去事实的假设。故选D。