A.
SELECT sname FROM student, sc WHERE student.sno = sc.sno AND cno = '1'
B.
SELECT sname FROM student WHERE sno IN(SELECT sno FROM sc WHERE cno = '1')
C.
SELECT sname FROM student WHERE EXISTS(SELECT * FROM sc WHERE sc.sno = student.sno AND cno = '1')
D.
SELECT sname FROM student WHERE EXISTS(SELECT * FROM sc WHERE cno = '1')