First of all,they may have come to this planet of ours thousands or millions of years ago

分类: 作业答案 • 2023-01-12 14:11:30

问题描述：

First of all,they may have come to this planet of ours thousands or millions of years ago
为什么用现在完成式have come to,后面不是有years ago.不用过去完成式had come to

答

因为这是may have come 是情态动词的完成时不属于现在完成时是对过去情况作出判断的所以可以和过去时间连用