题目:设有学生表 Student(学号,姓名,系名,课程号,成绩),查询至少选修了 4门课程的学生学号及平均成绩的正确语句是( )
A. SELECT 学号, AVG(成绩) AS 平均成绩 FROM Student GROUP BY 学号HAVING COUNT(课程号)>3
B. SELECT 学号, AVG(成绩) AS 平均成绩 FROM Student GROUP BY 课程号HAVING COUNT(课程号)>3
C. SELECT 学号, AVG(成绩) AS 平均成绩 FROM Student GROUP BY 学号HAVING COUNT(课程号)>4
D. SELECT 学号, AVG(成绩) AS 平均成绩 FROM Student GROUP BY 课程号HAVING COUNT(DISTINCT 学号)>3
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