She is the only one of the students able to answer this question.A. who isB. who areC. th

问题补充：

She is the only one of the students able to answer this question.

A. who is

B. who are

C. that is

D. that are

答案：

(答案→)A. who is

B. who are

C. that is

D. that are

解析：本题修饰一个表示人的代词one，是一个定语从句，修饰人关系词用who，who在从句中作主语，先行词为单数，故who后的be动词用is，故本题选A。