A、SELECT学号FROM score sc WHERE课程号="Cl"AND学号IN (SELECT学号FROM score sc WHERE课程号="C5")
B、SELECT学号FROM score sc WHERE课程号="Cl"AND学号= (SELECT学号FROM score sc WHERE课程号="C5")
C、SELECT学号FROM score sc WHERE课程号="Cl"AND课程号="C5"
D、SELECT学号FROM score sc WHERE课程号="Cl"OR课题号="C5"