By the year 2012,the world's population__seven billion,A may be B maybe C may is D may,

问题描述:

By the year 2012,the world's population__seven billion,A may be B maybe C may is D may,

A may be
这句话缺少谓语动词,所以用情态动词+动词原形 做谓语.
B只是副词 C is不是原形 D.缺少动词原形