单选题

一个查询语句执行后显示的结果为：1班 802班 753班 NULL，则最有可能的查询语句是（）

Question

A. SELECT AVG(成绩) FROM 成绩表 WHERE class<=3

B. SELECT AVG(成绩) FROM 成绩表 WHERE class<=3 GROUP BY class

C. SELECT AVG(成绩) FROM 成绩表 WHERE class<=3 order by class

D. SELECT AVG(成绩) FROM 成绩表 HAVING class <=3 GROUP BY class