有如此一道考试试题：
We took what he said literally, which _______ a mistake.
A. may be B. may have been
C. can be D. can have been
选项 C 和 D 可以排除，由于情态动词 can 表推断时一般不需要于一定句。但对于 A 和 B 呢？大家应该依据前面的过去式 took 来决定答案应选 B 吗？
1. 答案应选 B：
其依据确实是前面句子中的过去式 took，即依据 took 用的过去式可知，状况发生在过去，这说明后面句子的推断也是针对过去状况作出的，故用“情态动词+完成式”来表示。
2. 句子意思是：
We took what he said literally, which may have been a mistake. 我照字面意思来理解他所说的话，这可能是错的。
3. 类似使用方法如：
He may have lost his way. 他可能迷失方向了。
He may have been mistaken about what he saw. 他可能看错了。
She may have been sent to work elsewhere. 她可能被派到别处工作去了。
He may have been there a month ago. 他或许一个星期以前就去过那儿。
The injury may have caused brain damage. 受伤可能导致了脑损伤。
You may have noted that my address has changed. 你或许已经注意到我的地址变了。
I may have hurt your feelings but such was certainly not my intention. 我可能伤害了你的感情，但那绝不是我的意图。
He may have missed the train, in which case she won’t arrive for another hour. 他可能错过火车了，那样的话他就会还要等1个小时才会来。
