已知关系模式：sc(sno,sname,grade)，各属性含义依次为学号、课程名、分数。要查找“数据库”课分数最高的学生的学号，正确的SQL语句是( )。
A．SELECT sno FROM sc WHERE sname="数据库"AND grade=MAX(grad
B．SELECT sno FROM sc FOR sname="数据库"OR grade>=MAX(grad
C．SELECT sno FROM sc WHERE sname="数据库"AND grade=(SELECT MAX (grad FROM s
D．SELECT sno FROM sc FOR sname="数据库" OR grade=(SELECT MAX (grad FROM s