hadbeendoing是什麼時態

Nobody knew what they had been doing all these years.

沒有人知道他們這些年都在幹什麼。

Until this summer, China had been doing that carefully.

截止今年夏天，中國一直在審慎地這麼做。

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

在那時，他才意識到他一直在做的事。