20．If knowledge is power, ______ Sir Francis Bacon wrote in 1579, ______ perhaps creativity can be described as the ability to use that power.

A．what; and　 　 B．as; then　　　 C．which; and　　 D．that; then

19．The WenChuan earthquake in 2008 is believed ______ more than 70,000 people and made thousands homeless, ______ it perhaps the most destroying tsunami in history.

A．to kill; making　　 　　　　　　　 B．to have killed; making　

C．having killed; to make　 　　　　　　　　　　　　　 D．killing; made

18．_____ I can’t understand was _____ there are more and more junk-emails on the Internet.

A．What; why 　　 B．That; what　 　 C．What; because　 D．Why; that

17．-What were you doing when Tom came to see you?

-I _____ on my overcoat and _____ to visit a friend of mine.

A．have just put; leaving　　　　 　 B．was put; was left

C．had just put; was leaving　　　 　 D．was putting; left

16．-It’s a long time ______ I saw you last.

-Yes, and what a pity it is now that it will be a long time _____ we see each other again.

A．before; since　 B．since; when　　 C．since; before　 D．when; before