( )of the students in John’s class are in ( )

( )of the students in John's class are in ( )
A.one-half,the twenties B.Half ,the twenties C.half,their twenties D.A half ,their twenties

答案是C/ D --------- HALF -- - - IN THEIR TWENTIES
1 half of -- - - 一半的 + 名词复数形式 --------作主语时,谓语动词是are.
2 in their twnties == between 21 and 29 years old