在学生选课数据库中有学生表student(sno,sname,ssex,sage,sdept),课程表course(cno,cname)及学生选课表sc(sno,cno,grade),其中sno是学号,sname是姓名,ssex是性别,sage是年龄,sdept是系别,cno是课程号,cname是课程名,grade是成绩。以下()SQL语句可以实现查询“CS”系并且年龄超过20岁的学生姓名。
A.select sname from student where sdept=’CS‘ and sage>20
B.select sname from student where sdept=’CS‘ intersect select sname from student where sage>20
C.select sname from student where sdept=’CS‘ except select sname from student where sage<=20
D.select sname from student where sdept=’CS‘ union select sname from student where sage>20