21.
(A)upon
(B) for
(C) with
(D) to

17. (A)debilitating (B) debilitated (C) debilitatedly (D) debilitate 

18. (A)thus (B) yet (C) so (D) because

19. (A)does not eradicate (B) did not eradicate (C) has not eradicated (D) has not been eradicated

20. (A)being self-sufficient (B) was self-sufficient (C) will be self-sufficient (D) has been self-sufficient

22. (A)contributing (B) contributed (C) contribute (D) being contributed

複選題23. (A)Our ancestors taught us many things so that we lead our lives today. (B) But the difference today is how we get our information. (C) But a complex society is not a place that is suitable for our ancestors. (D) Yet the living of our ancestors could not predict our future.

複選題24. (A)Initially, many people were excited about this opening up to multiple voices. (B) It will be hard to address any of the problems that the world now faces. (C) But such debates are happening less and less. (D) But our ancestors might not agree with some of these voices.

複選題25. (A)Newspapers are printed and distributed usually daily or weekly and that contains news, articles of opinion, features, and advertising. (B) Newspaper organizations that publish newspapers are mushrooming. (C) Newspapers have been a trusted source of news for many people for decades. (D) People have been distributing information from different sources of newspapers.

複選題26. (A) Yet Wikipedia is also a trusted source of news. (B) Wikipedia is a work that contains information on all branches of knowledge. (C) First, Wikipedia treats comprehensively a particular branch of knowledge usually in articles arranged alphabetically often by subject. (D) Yet Wikipedia itself is far from perfect.

複選題27. (A)Very rarely do they worry that fundamental things they believe themselves may be wrong. (B) Information technology is the practical application of knowledge especially in a particular area. (C) Very often, technology is seen as a manner of accomplishing a task especially using technical processes, methods, or knowledge. (D) To believe is to have a firm conviction as to the goodness, efficacy, or ability of something.