单项选择题假定有三个关系,学生关系S、课程关系C和学生选课关系SC,它们的结构如下: S(S#,SN,Sex,Age,Dept),C(C#,CN),SC(S#,C#,Grade)。其中,S#为学生号,SN为姓名,Sex为性别,Age为年龄,Dept为系别,C#为课程号,CN为课程名,Grade为成绩。检索选修课程“C2”的学生中成绩最高的学生的学号,正确的SQL.语句是()。
A.SELECT S#FROM SC WHERE C#="C2" AND Grade IN (SELECT Grade FROM SC WHERE C#="C2")
B.SELECT S# FROM SC WHERE C#="C2" AND Grade>= (SELECT Grade FROM SC WHERE C#="C2")
C.SELECT S# FROM SC WHERE C#="C2" AND Grade>=ALL (SELECT Grade FROM SC WHERE C#="C2")
D.SELECT S# FROM SC WHERE C#="C2" AND Gtade NOT IN (SELECT Grade FROM SC WHERE C#="C2")