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 my score where sum(score)<90 group by paper_id B.select paper_id from my score group by paper_id having avg(score)<90 C.select paper_id from my score where avg(score)<90 D.select paper_id from my score where avg(score)<90 group by paper_id