had后加动词过去分词。

用于过去完成时，had+done。过去完成时表示的是站在某个过去的时间点，对这个时间点之前发生的一个或一系列动作的总结。

例：When they reached there，the ship had set off.

当他们到达那里的时候，船已经开了。

相关介绍

We had a day out in the country.

我们在乡下玩了一天。

He had to go to the hospital for treatment.

他不得不去医院接受治疗。

Had I known that I would never have come.

要是早知道，我绝不会来的。

He had to go to hospital for treatment.

他不得不去医院接受治疗。