针对表 Student(sno, sname, ssex, sage, sdept)，其中 sno 为学号，sname 为姓名，ssex 为性别，sage 为年龄，sdept 为系别。查询女生平均年龄超过 20 岁的系别以及女生平均年龄( )。
选项：

A:

select sdept ,avg(sage) from student group by sdept having ssex='女' and avg(sage) >20

B:

select sdept ,avg(sage) from student where ssex='女' group by sdept having avg(sag e) >20

C:

select sdept ,avg(sage) from student where ssex='女' group by sdept

D:

select sdept ,avg(sage) from student group by sdept having avg(sage) >20