21、 The brains of human beings have developed quite a lot _________ we have obtained plenty of information available for further research and studies..

     A. when                   B. which        C. that                   D. where

20、They needn’t have spent so much energy and time testing the materials, most of ________ conform to the requirements.

A. what          B. whom        C. which        D. them  

19、 How’s your visit to the Magic Valley? Is it really magic?

It ________ be, but you can’t avoid seeing a lot of people titer here and there.

A. should        B. would        C. must            D. will  

18、 Come on, Alan, please give me some ideas about the physical problem.

I’m sorry, Jack. With my mind ________ so much work, you see, I almost break down.

A. to fill in      B. filling up            C. filled with           D. being filled of   

17、

－_____ you _______ the visitors around our library yet?

－Yes. We had a great time there.

A. Do; show        B. Did; show            C. Had; shown              D. Have; shown

16、 How was the televised youth singing competition last night?

Terrific! Scarcely _______ so large an audience around the country.

A. a competition attracted             B. did a competition attract

C. a competition did attract           D. attracted a competition           

15、Since Jane ______ downloaded a virus into her laptop, she cannot open the file now.

A. horribly             B. accidentally        C. readily        D. irregularly 

14、It is reported scientifically that a living cell can be _________ for a thousand years at minus 130℃.

A. preserved   B. protected           C. developed          D. spared      

13、 Come on, Jack. Tell me how you keep so healthy a body and so clever a head.

Well, you see. Partly my evening ______ includes jogging in the park and reading books before bedtime.

A. action        B. routine              C. regulation          D. drill          

12、 When did ______ picnic take place?

It was on ______ pleasant sunny morning in May, and everyone enjoyed himself very much.

A. the; the             B. an; /                  C. an; the              D. the; a