had worked是什么时态

had worked这个结构是过去完成时态，表示在过去某个具体时间之前发生的动作。

如：They had worked for twelve hours by last night. 到昨晚为止，他们己经工作了十二小时。工作十二小时这个动作发生在昨晚之前，所以要用过去完成时态had worked。