单项选择题
A.dropB.changeC.modifyD.rename
A.select sex，count（*）from student group by sexB.select sex，sum（*）from student group by sexC.select sex，sum（sex）from student group by sexD.select sex，count（sex）from student order by sex
A.一对一关系B.一对多关系C.多对一关系D.多对多关系