grade是成绩信息表,curriculum是课程信息表,建立一个视图v_cavg,该视图包括了课程编号和(该课程的)平均成绩两个字段,正确的SQL语句是( )。 A. Credate View v_cavg AS 课程编号,AVG(分数)AS 平均成绩 From grade Group by 课程编号 B. Credate View v_cavg AS SELECT课程编号,AVG(分数) From grade Group by 课程编号 C. Credate View v_cavg AS SELECT课程编号,AVG(分数)AS 平均成绩 From grade Group by 课程编号 D. Credate View v_cavg AS SELECT课程编号,AVG(分数)AS 平均成绩 From curriculum Group by 课程编号