以下( )操作实现了student表与sc之间的自然连接。 (2.0)
选项：

A:select student.* , sc.* from student , sc where student.sno=sc.sno
B:select student.* , cno, grade from student , sc where student.sno=sc.sno
C:select student.sno, sname,ssex,sage,sdept , cno, grade from student , sc where student.sno=sc.sno
D:select student.* , cno, grade from student join sc on student.sno=sc.sno