单项选择题
关系SC(Sno，Cno，Grade)表示学号，课程号，成绩。现要查询平均分在90分以上的学生的学号和平均成绩，正确的语句是______。
A．SELECT Sno，AVG(Grade)FROM SCWHERE AVG(Grade)＞=90GROUP BY Sno
B．SELECT Sno，AVG(Grade)FROM SCGROUP BY SnoHAVING AVG(Grade)＞=90
C．SELECT Sno，AVG(Grade)FROM SCWHERE AVG(Grade)＞=90ORDER BY Sno
D．SELECT Sno，AVG(Grade)FROM SCGROUP BY CnoHAVING AVG(Grade)＞=90