第4单元，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;

正确答案：SELECT 学号， AVG(成绩) AS 平均成绩 FROM student GROUP BY 学号 HAVING COUNT(课程号)>3;