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。
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。
Everybody knew what he had been doing all those years.
大家都知道那些年他在做什么。
It was, after all, what we had been doing all along.
毕竟，我们一直在做这一行。
I had been doing what you're almost certainly doing now.
我做的是你们肯定现在在做的。