多选题

表结构如下： CREATE TABLE `score` ( ...

Question

表结构如下：

CREATE TABLE `score` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `sno` int(11) NOT NULL,
   `cno` tinyint(4) NOT NULL,
   `score` tinyint(4) DEFAULT NULL,
   PRIMARY KEY (`id`)
 ) 

以下查询语句结果一定相等的是（）

A.SELECT sum(score) / count(*) FROM score WHERE cno = 2

B.SELECT sum(score) / count(id) FROM score WHERE cno = 2

C.SELECT sum(score) / count(sno) FROM score WHERE cno = 2

D.SELECT sum(score) / count(score) FROM score WHERE cno = 2

E.SELECT sum(score) / count(1) FROM score WHERE cno = 2

F.SELECT avg(score) FROM score WHERE cno = 2

A. A,E,F

B. A,D,F

C. A,B,C,D

D. D,F

E. A,B,E,F

F. A,B,C,E