在学生选课数据库中，查询平均成绩大于等于60分的同学，SQL语句为（       ）
A、SELECT Sno, AVG(Grade) FROM SC GROUP BY Sno HAVING AVG(Grade)>=60;
B、SELECT Sno FROM SC WHERE Grade>=60 GROUP BY Sno;
C、SELECT Sno, Grade FROM SC GROUP BY Sno HAVING AVG(Grade)>=60;
D、SELECT Sno FROM SC GROUP BY Sno HAVING Grade >=60;