One third of the class agreed to be volunteers to help the aged this vocation.A. areB. is

问题补充：

One third of the class agreed to be volunteers to help the aged this vocation.

A. are

B. is

C. has

D. have

答案：

A. are

B. is

C. has

(答案→)D. have

解析：考查主谓一致。句意：这个假期这个班三分之一的学生同意作为志愿者帮助老年人。本句中class为集合名词，表示复数含义，当前面有分数修饰时，后面谓语动词与名词保持一致，故选D。