If human beings had been a bit less greedy and cruel, more birds and animals dying out.
A. ought to avoid
B. could have been avoided
C. should have avoided
D. might have avoided
网友回答
A. ought to avoid
B. could have been avoided
C. should have avoided
(答案→)D. might have avoided
解析：本题涉及虚拟语气的使用，从if引导的从句分析可以知道与过去相反，should have done表示本来不应该但实际上干了，不符合题意。