用SQL语句检索选修课程在5门以上(含5门)的学生的、姓名和平均成绩,并按平均成绩降序排序,正确的命令是( )。 A)SELECT S.,姓名,平均成绩FROM S,SC; WHERE S.=SC.; GROUP BY S.HAVING COUNT(﹡)>=5 0RDER BY平均成绩DESC B)SELECT,姓名,AVG(成绩)FROM S,SC; WHERE S.=SC.AND COUNT(﹡)>=5; GROUPBYORDERBY 3 DESC C)SELECT S.,姓名,AVG(成绩)平均成绩FROM S,SC; WHERE S.=SC.AND COUNT(﹡)>=5; GROUP BY S.ORDER BY平均成绩DESC D)SELECT S.,姓名,AVG(成绩)平均成绩FROM S,SC; WHERE S.=SC.; GROUP BY S.HAVING COUNT(﹡)>=5 0RDER BY 3 DESC