A．SELECT sname FROM student，SELECT cno，grade FROM sc WHERE studensno＝ssno
B．SELECT sname，cno，grade FROM student，course WHERE studensno＝courscno
C．SELECT sname，cname，grade FROM student，course，sc WHERE studensno＝ssno and scno＝course，cno
D．SELECT sname，cno，grade FROM student，sc WHERE studensno＝ssno