问题
选择题
If they had known what was coming next, they __ their mind.
A．may change
B．could change
C．must have changed
D．might have changed
答案
答案：D
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。