A 形式
to have been+现在分词：
He seems to have been spying for both sides.
他似乎一直在为两方面搞秘密情报。
B 用法
主要用于助动词之后和appear，seem之后，但也可以用在happen， pretend以及believe， know， report， say， understand的被动式之后：
He says he was talking to Tom.
He couldnt have been talking to Tom.Tom wasnt there.
他说他当时在跟汤姆说话。
他当时不可能在和汤姆说话。汤姆当时不在那里。
I was following Peter closely.
You shouldnt have been following him closely;you should have left a good space between the two cars.
当时我正紧紧地跟着彼得。
你不应该紧跟着他;而应该使两车之间保持相当的距离。
He appears to have been waiting a long time.相当于：
It appears that he has been waiting a long time.
看来他已经等了很久了。
He pretended to have been studying.相当于：
He pretended that he had been studying.
他假装一直在学习的样子。