有关系s(s#,sname,sage),c(c#,cname),sc(s#,c#,grade)。其中s#是学生号,sname是学生姓名,sage是学生年龄, c#是课程号,cname是课程名称。要查询选修“access”课程的年龄不小于20的全体学生姓名的sql语句是 select sname from s,c,sc where子句。这里的where子句的内容是( )。
a.s.s# = sc.s# and c.c# = sc.c# and sage>=20 and cname=‘access’
b.s.s# = sc.s# and c.c# = sc.c# and sage in>=20 and cname in ‘access’
c.sage in>=20 and cname in ‘access’
d.sage>=20 and cname=’ access’