He can't have been.He must have been.不是说单三用has吗?这里怎么用的have?

He can't have been.He must have been.不是说单三用has吗?这里怎么用的have?
He can't have been.He must have been.不是说单三用has吗?
这里怎么用的have?

He can't have been.He must have been.不是说单三用has吗?这里怎么用的have?
正确答案为：
在情态动词（can't,must）后面动词要用原形have.
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前有情态动词can

can是情态动词，后面接原形

can't +动词原形

情态动词后加原型

前面有can't 情态动词后动词用原型

因为can 和 must 是情态动词，后面的动词保持原型

因为接在否定式后面，用原形

这里的谓语是can not和must。have不是谓语，故不适用单三

can 跟must是情态动词

情态动词后面直接加动词原形，比如还有：
can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would) .

情态动词后加动词原型

情态动词后面加动词原型