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问题: 作业求助 英语单选

by the middle of the 21st century,the vast majority of the world's population __in cities rether than in the country.
a.are living
b.will be living
c.have lived
d.will have lived

解答:

答案选D。

时间状语为“by(截止到)+ 表示将来的时间名词短语”,主句要用将来完成时。