在MySQL中，STUDENT_GRADES 表有这些列：
STUDENT_ID INT
SEMESTER_END DATE
GPA FLOAT
以下哪种说法能查询每学期平均学分绩点（GPA）最高？( )
SELECT MAX(GPA) FROM STUDENT_GRADES WHERE GPA IS NOT NULL
SELECT GPA FROM STUDENT_GRADES GROUP BY SEMESTER_END
SELECT MAX(GPA) FROM STUDENT_GRADES GROUP BY SEMESTER_END
SELECT TOP 1 GPA FROM STUDENT_GRADES GROUP BY SEMESTER_END
都不行
