could原型是哪个

could原型是:can

His subtlety could not avail him here .他精明机智在这里无济于事了。

I could hear them crying out to one another .我听得见他们相互呼应。

He was so pressing i could n't refuse .他这样坚持，我实在难以拒绝。

He could feel the menace of the spreading .他能感到这种膨胀的威胁。

You could at least have sent a card .你本来至少可以寄张明信片来吧。