多年来，医生们一直在研究这个问题。

The children have bee watching TV all morning. 孩子们一上午一直在看电视。

She has been waiting for her boss for almost an hour. 她等她的老板等了将近一个小时。

第三部分：练习

1. 单项填空

1 How can you possibly miss the news? It _______ on TV all day long. （2004北京春）

　A. has been B had been C was D will be

2 I arrived late; I _____ the road to be so icy. （2004北京春）

　A. wouldn't expect B haven't expected C hadn't expected D wasn't expecting

3 Although he has lived with us for years, he ______ us much impression. (2004上海春)

　A hadn't left B didn't leave C doesn't leave D hasn't left

4 ―Sorry, Joe. I didn't mean to....

―Don't call me "Joe". I'm Mr. Parker to you, and ______ you forget it! （2003全国）

　A do B didn't C did D don't

5 All morning as she waited for the medical report from the doctor, her nervousness_______.（2003全国）

　A has grown B is growing C grew D had grown

6 Why don't you put the meat in the fridge? It will _______ fresh for several days. （2003全国）

　A be stayed B stay C be staying D have stayed

7 ―_______ David and Vicky _______ married? (2003北京)

―For about three years.

　A How long were; being B How long have; got

　C How long have; been D How long did; get

8 Come and see me whenever_______. (2003北京)

　A you are convenient B you will be convenient]

C it is convenient to you D it will be convenient to you

9 ―When will you come to see me, Dad?

―I will go to see you when you ______ the training course. (2003北京)

　A will have finished B will finish C are finishing D finish

10 When and where to go for the on-salary holiday _______ yet. (2003北京春)