六、can (could) +have +-ED 分词：用于表示过去的时间，说明某事可能或不可能已发生：

I simply can't understand how he could have made such a mistake. 我简直不明白他怎么会犯那样的错误。

He is an hour late —He can have been delayed by fog.Of course, that's a possibility.

他迟到了 1 小时，可能因为大雾而耽搁了。

This poem can't have been written by her.She is only five. 这诗不可能是她写的，她才 5 岁。