查询所有年龄在20岁以下的学生姓名及其年龄,以下正确的是( )。
A.
SELECT Sname,Sage FROM tb_student WHERE Sage <=20;
B.
SELECT Sname,Sage FROM tb_student WHERE NOT Sage <20;
C.
SELECT Sname,Sage FROM tb_student WHERE NOT Sage >20;
D.
SELECT Sname,Sage FROM tb_student WHERE Sage <20;