大学英语：过去完成进行时

　　1.概念
　　(1)表示到过去某个时刻此动作还在进行。
　　（2）用在从句中，从句的动作发生在主句的动作之前而对其有影响。
　　①At last the bus came,  I had been waiting for half an hour.
　　②Until then she had been loving her daughter.
　　③Her eyes were red. It was obvious she had been crying.
　　④I heard you’d been looking for me.wｗw.ExamＷ.CoM
　　2.基本结构
　　S+had+been+doing注意其否定、疑问形式。
　　3.现在完成进行时/过去完成进行时
　　He’s been smoking for 20 years.
　　He’s still smoking.
　　He’d been smoking for 20 years when he decided to give it up.
　　至过去某个时刻还在进行某动作。
　　4.过去完成时/过去完成进行时
　　By last week she had collected 2000 stamps.(已完成)
　　She had been collecting stamps all these years.(未必完成)
　　She had been painting the door all afternoon.(未必完成)