--Dose Liu Hui serve in the army?--No,but he ( ) in the army for three years.A served B has served C is aerving D would serve
问题描述：
--Dose Liu Hui serve in the army?
--No,but he ( ) in the army for three years.
A served B has served C is aerving D would serve
答
A
答
选B，
答
B for three years就是现在完成时的标志，所以选B
答
B现在完成时 用has been的形式
答
选A
--Dose Liu Hui serve in the army?
既然回答的是NO,说明他现在已经不在部队了,不可能用现在完成时,因为现在完成时表示持续到现在的意思,应选A