By the time I got outside,the bus had already left 这是什么时态啊

问题描述:

By the time I got outside,the bus had already left 这是什么时态啊

had already left 过去完成时
当我出去时,公交车已经开走了.
had already 说明是完成时
而had又是过去时.
说明就是过去完成时