用法：
1、表示某一動(dòng)作在過(guò)去某一時(shí)刻之前已完成。例如:
He had gone to bed by 10:00 last night.
昨夜十點(diǎn)鐘之前他已上床去睡了。
2、與一般過(guò)去時(shí)搭配，表達(dá)某一動(dòng)作在過(guò)去的動(dòng)作發(fā)生時(shí)已完成。例如：
The train had started when I got to the station.
當(dāng)我到達(dá)車站時(shí)火車已開(kāi)走了。