针对学生选课数据库S_T,以下()操作实现了student表与sc之间的自然连接。
A、select student.* , cno, grade from student join sc on student.sno=sc.sno
B、select student.* , sc.* 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 , sc where student.sno=sc.sno