问题补充：
He is the only one of the students who a winner of schoolarship for three years.
A. is
B. has been
C. are
D. have been
答案：
A. is
(答案→)B. has been
C. are
D. have been
解析：句意：他是唯一的一个赢得三年奖学金的学生。这里who引导的是定语从句，它在从句中作主语，因为先行词被the only修饰，所以从句的谓语动词应该用单数，故排除CD；又因为从句中有时间状语for three years表示他是奖金的获得者从过去一直持续到现在，所以应该用现在完成时，故选B。
