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。放在间接引语或虚拟语气中时它的时态不能再向前推，向后推是现在完成进行时。
双语例句
1、Benjamin was forced to admit what he had been doing．
本杰明被迫承认他所做的一切。
2、I had told people what he had been doing, so now the police were onto him.
我已将他的所作所为告诉了别人，因此现在警方正在追查他。
3、Until this summer, China had been doing that carefully.
截止今年夏天，中国一直在审慎地这么做。
4、I had been doing the work for two hours when the teacher came.
老师来时那件工作我已做了两小时了。&当时工作尚未完成，所以老师来了我还继续在做。
5、Everybody knew what he had been doing all those years.
大家都知道那些年他在做什么。