20. ________ I cannot understand is ________ she wants to resign her present job.

A. What; why 　　　　　　 　　　　B. Which; how 　 　C. That; why　 　　　 　D.What; because

19. ________ the website of the Fire department in your city, and you will learn a lot about firefighting.

A. Having searched 　　B. To search 　　　 　　　C. Searching 　　　　　 　　D. Search

18. He appears to be optimistic, but, ________, he is quite pessimistic.

A. in other words 　　　　　　　 　　B. on one hand　 　　 C. for one thing 　　 　　D. as a matter of fact

17. ________ you may have, you should gather your courage to face the challenge.

A. However a serious problem 　　　　　　　　B. What a serious problem

C. However serious a problem　　　　　　 　　D. What serious a problem