Until this summer, China had been doing that carefully.

　　截止今年夏天，中國一直在審慎地這么做。

　　I had been doing the work for two hours when the teacher came.

　　老師來時那件工作我已做了兩小時了。&當時工作尚未完成，所以老師來了我還繼續在做。

　　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.

　　畢竟，我們一直在做這一行。

　　I had been doing what you're almost certainly doing now.

　　我做的是你們肯定現在在做的。