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;