学生关系student的主码是sno，课程关系course的主码是cno，选课关系sc的主码是(sno，cno)。 查找选修课程名为‘数据库’的学生姓名和成绩，正确的答案中应有几个记录

A．SELECT sname FROM student，SELECT cno，grade FROM SC WHERE student.sno=SC.sno
B．SELECT sname，cno，grade FROMstudent，course WHEREstudent.sno=course.Cno
C．SELECT sname，cname，grade FROMstudent，course，SC WHEREstudent.sno=SC.snoandSC.cno=course，cno
D．SELECT sname，cno，grade FROMstudent，SC WHEREstudent.sno=sc.sno

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 BY S.S#
D．SELECT S.S#，SNAME FROM S WHERE S.S# IN (SELECT SC.S# FROM SC WHERE C#=’C2’)