针对数据库S_T，以下创建视图的命令不正确的是（）。

A、create view view1 as select sno, avg(grade) from sc group by sno

B、create view view2 as select sno, sname, sdept from student where sdept='CS'

C、create view view3 as select sno, sage+20 from student where ssex='女'

D、create view view4 as select student.sno, sname, sc.sno, cno, grade from sc,student where sc.sno=student.sno and cno='1'