课程表结构如下SC(Sno, Cno, Cname, Grade),其中列Cno和Sno的数据类型均为varchar(20),Cname为nvarchar(20),Grade数据类型为smallint。查询'007'号课程的最高分、最低分和平均分,对应的SQL语句可以是( )。 A. SELECT MAX(Grade), MIN(Grade), AVG(Grade) FROM SC WHERE Cno='007' ; B. SELECT MAX(Grade), MIN(Grade), AVG(Grade) FROM SC WHERE Cno in ('007'); C. SELECT max(Grade), min(Grade), avg(Grade) FROM SC where Cno='007'; D. SELECT MAX(Grade), MIN(Grade), sum(Grade) FROM SC WHERE Cno='007';