If they had known what was ing next, they their mind.
A. may change
B. could change
C. must have changed
D. might have changed
网友回答
A. may change
B. could change
C. must have changed
(答案→)D. might have changed
解析：考查情态动词。if引导的条件状语从句与过去是相反，主句中要用would/should might have done. 而must have done表示一定已经做了某事。