查询全体学生的情况，查询结果按所在系升序排列，同一系中的学生按年龄的降序排列（）Aselect*fromstudentorderbydepart，agedescBselect*fromstudentorderbydepartandagedescCselect*fromscorderbydepart，agedescDselect*fromscorderbydepartandagedesc