17. Either the teachers or the pesident _________ the meeting.
A. attends
B. attend
C. are attending
D. have attended
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18. The number of articles published on smoking ________ amazing.
A. is
B. are
C. were
D. have been
19. In that country, the rich ________ richer, the poor, poorer.
A. become
B. has become
C. becomes
D. is becoming
20. Three-fourths of the buildings ________ during the war.
A. was destroyed
B. is destroyed
C. were destroyed
D. has been destroyed
自动满足基尔霍夫第一定律的电路求解法是回路电流法。
A. 对
B. 错
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