He could have e to help us ,but
网友回答
这是一个虚拟语气中的常考句型,要记住.could have done的意思是“本可以做某事（而实际上没做）”.句型：Sb could have done sth,but + 一般过去时.的意思为：某人本可以做某事的,但（实际情况是）…….由于后句讲述的是真实情况,故用一般过去时.
关于你的补充问题：
He could have e to help us后的反意疑问句的tag理论上是didn't he,只是此句中He could have e to help us应该是一个确定的判断,一般不会用反意疑问句形式.
如果是猜测,则一定是didn't he.请看下列例句：
He could not have e to help you,did he?
He must have e to help you,didn't he?
He might have e to help you,didn't he?
祝周末愉快!
======以下答案可供参考======
供参考答案1:
虚拟语气，后句时态过去
供参考答案2:
could have e to是虚拟语气，用过去时he didn't 表过去没有做的事实。