答案：D

题目分析：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 coming next=If  they had known what was coming 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。