1 . I can’t imagine what air we would be breathing in if we __________ anything to stop air pollution.

A．hadn’t done	B．didn’t do
C．haven’t done	D．don’t do

2 . A killer whale at Sea World Orlando jumped out of its tank on Wednesday and fatally attacked a worker as horrified visitors _______.

A．has been looking up

B．looked on

C．had looked off

D．was looking in

3 . — I’ve never seen you so rude!
— I _____ something I shouldn’t have, but I didn’t mean that．

A．have said	B．had said
C．did say	D．was saying

4 . My cousin went to Canada two years ago. He ______ there for a few months and then went to America.

A．worked

B．would work

C．would be working

D．has been working

5 . I ________ him in time, otherwise he would have fallen off the bike.

A．had supported	B．supported
C．have supported	D．support

6 . — Have you read the novel?
— Yes. I ________ it three times while I was in university.

A．had read	B．read
C．have read	D．was reading

7 . More than one doctor _____ involved in the rescue that took place after the earthquake．

A．was

B．is

C．were

D．are

8 . Our English teacher , having explained to us how to design a project, allowed us   a whole week’s preparation and then ______the class.

A．to dismiss	B．dismissed
C．dismissing	D．having dismissed