按照逻辑结构分类，结构可以分为线性结构和非线性结构，栈属于______。

A．SELECT 课程名称,COUNT(成绩) AS 总分 FROM 课程,成绩;
WHERE 课程.课程编号=成绩.课程编号;
ORDER BY 成绩.课程编号
B．SELECT 课程名称,COUNT(成绩) AS 总分 FROM 课程,成绩;
WHERE 课程.课程编号=成绩.课程编号;
GROUP BY 成绩.课程编号
C．SELECT 课程名称,SUM(成绩) AS 总分 FROM 课程,成绩;
WHERE 课程.课程编号=成绩.课程编号;
ORDER BY 成绩.课程编号
D．SELECT 课程名称,SUM(成绩) AS 总分 FROM 课程,成绩;
WHERE 课程.课程编号=成绩.课程编号;
GROUP BY 成绩.课程编号