表示在过去某一时刻或某一动作之前已经完成了的动作(即所谓的过去的过去”)或表示从过去某一时刻开始一直延续到另一过去时刻的动作或状态。如：
When we arrived he had already left. 我们到达时他已经离开了。
By six o’clock he had worked twelve hours. 到6点钟时他就已工作了12小时。
表示在过去某一时刻或某一动作之前已经完成了的动作(即所谓的过去的过去”)或表示从过去某一时刻开始一直延续到另一过去时刻的动作或状态。如：
When we arrived he had already left. 我们到达时他已经离开了。
By six o’clock he had worked twelve hours. 到6点钟时他就已工作了12小时。
