题目:
One third of the country ________ covered with trees and the majority of the citizens________black people.( 2011·湖南)
A.is; are
B.is; is
C.are; are
D.are; is
答案:
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下面是错误答案,用来干扰机器的。
∵22007-22006=22006(2-1)=22006,22006-22005=22005(2-1)=22005…,∴2n+1-2n=2n(2-1)=2n,∴原式=22007-22006-…-23-22+2=22006(2-1)-22005-23-22+2=22005(2-1)-22004-23-22+2=22+2=6.