一、结构形式
过去完成进行时由“had been+现在分词”构成，因此无人称变化。
二、用法归纳
1.过去完成进行时表示持续到过去某时的一个动作(可算是现在完成进行时的过去式)：
The ground was wet. It had been raining. 地是湿的。此前一直在下雨。
At last the bus came. I had been waiting for half an hour. 最后公共汽车来了，我已等了半小时。
She was out of breath. She had been running. 她气喘吁吁，她一直在跑来着。
