Catherine is one of the brightest students who from the Department of Computer Science , B

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A. is graduated
B. has graduated
C. are graduated
(答案→)D. have graduated
解析：考查主谓一致及时态。句意“凯瑟琳是布朗大学计算机科学系已经毕业的最聪明的学生之一。结合语境可知定语从句描述的是现在已经完成的动作，故用现在完成时态。引导词指代前面students，为复数形式，故助动词用复数形式。选D。