检索选修课程“C2”的学生中成绩最高的学生的学号。正确的SELECT语句是（）。

A.SELECT SNO FROM SC WHERE CNO='C2' AND GRADE >=（SELECT GRADE FORM SC WHERE CNO='C2'）;

B.SELECT SNO FROM SC WHERE CNO='C2' AND GRADE IN（SELECT GRADE FORM SC WHERE CNO='C2'）;

C.SELECT SNO FROM SC WHERE CNO='C2' AND GRADE NOT IN（SELECT GRADE FORM SC WHERE CNO='C2'）;

D.SELECT SNO FROM SC WHERE CNO='C2' AND GRADE >= ALL（SELECT GRADE FORM SC WHERE CNO='C2'）;

正确答案：SELECT SNO FROM SC WHERE CNO='C2' AND GRADE >= ALL（SELECT GRADE FORM SC WHERE CNO='C2'）;