has been doing与had been doing,这两个时态分别代表怎样的概念,表示怎样的动作发生,用于何种情况,请大家分别具体解释一下它们所用的场合
问题描述：
has been doing与had been doing,这两个时态分别代表怎样的概念,表示怎样的动作发生,用于何种情况,请大家分别具体解释一下它们所用的场合
答
has been doing表示动作到现在为止一直在做
I have been waiting for you for an hour.
had been doing表示动作到过去某一时刻为止一直在做
I had been waiting for you for an hour until you finally reached.