had been doing这是过去完成进行时；表示从过去的某一个时间点开始做某事一直持续到过去的某个时间点并且仍在进行。例句：I had been looking for it for days before I found it.这东西我找了好多天才找着的。
特别含义
1、尚未完成：
He had been writing the novel．（他没有完成它）
2、企图：
He had been studying the meaning of this proverb．（他一直在努力学习它）
3、未得结果：
We had been studying what our enemy had said．（但我们不能理解）
4、最近情况：
He had been quarrelling with his wife．（近来）
5、情绪：
What had he been doing？（不耐烦）