A.SELECT S.S#,SNAME FROM S WHERE S.S#=(SELECT SC.S# FROM SC WHERE C#=/'C2/')
B.SELECT S.S#,SNAME FROM S,SC WHERE S.S#=SC.S# AND C#=/'C2/'
C.SELECT S.S#,SNAME FROM S,SC WHERE S.S#=SC.S# AND C#=/'C2/'ORDER BYS.S#
D.SELECT S.S#,SNAME FROM S WHERE S.S# IN(SELECT SC.S# FROM SC WHERE C#=/'C2/')