单选题

某网站的数据库有一个试卷表，希望找出试卷平均得分小于90的所有试卷。

Question

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