在关系SC中,查询学习课程号为'OB',且成绩在60至90之间的学生学号的正确的 SQL命令是
A. SELECT SNO FROMSC WHERE CNO='DB' AND GRADE BETWEEN 60 AND 90
B. SELECT SNO FROM SC WHERE CNO='DB' OR GRADE BETWEEN 60 AND 90
C. SELECT SNO FROM SC WHERE CNO='DB' AND GRADE>=60 AND 90
D. SELECTSNO FROM SCWHERECNO='DB' AND GRADE<=60 AND GRADE>=90