hadbeendoing是什么时态

Nobody knew what they had been doing all these years.

没有人知道他们这些年都在干什么。

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。

At that point, he realized what he had been doing all along.

在那时，他才意识到他一直在做的事。