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;