现有学生成绩表，成绩表中保存的字段如下：student_id, 学生学号student_name, 学生姓名course_

A.select student_id,student_name,sum(score) from student where score＜60 order by score;

B.select distinct student_id,avg(score) from student where score＜60 order by avg(score);

C.select student_id,student_name,avg(score) av from student where score＜60 group by student_id order by av asc;

D.select student_id,student_name,avg(score) av from student group by student_id where score＜60 order by av asc;