[问答] 检索选修四门以上课程的学生总成绩，并要求按总成绩的降序排列出来。正确的SELECT语句是（）。 A.SELECT SNO, SUM（GRADE）FROM SC GROUP BY SNO ORDER BY 2 DESC HAVING COUNT（*）>= 4; B.SELECT SNO, SUM（GRADE）FROM SC GROUP BY SNO HAVING COUNT（*）>=4 ORDER BY 2 DESC; C.SELECT SNO, SUM（GRADE）FROM SHAVING COUNT（*）>=4 GROUP BY SNO ORDER BY 2 DESC; D.SELECT SNO, SUM（GRADE）FROM SC ORDER BY 2 DESC GROUP BY SNO HAVING COUNT（*）>=4;