问题
某网站的数据库有一个成绩表myscore，希望找出成绩表中平均得分小于90的所有试卷()。
A:select paper_id from myscore where sum(score)< 90 group by paper_id
B:select paper_id from myscore group by paper_id having avg(score)< 90
C:select paper_id from myscore where avg(score)<90
D:select paper_id from myscore where avg(score)<90 group by paper_id
B:select paper_id from myscore group by paper_id having avg(score)< 90
C:select paper_id from myscore where avg(score)<90
D:select paper_id from myscore where avg(score)<90 group by paper_id
正确答案是：
