有如下的SQL语句。
Ⅰ. SELECT sname FROM s, sc WHERE grade<60
Ⅱ. SELECT sname FROM s WHERE sno IN(SELECT sno FROM sc WHERE grade<60)
Ⅲ. SELECT sname FROM s, sc WHERE s.sno=sc.sno AND grade<60
若要查找分数(grade)不及格的学生姓名(sname),则以上正确的有哪些?( )
A. Ⅰ和Ⅱ
B. Ⅰ和Ⅲ
C. Ⅱ和Ⅲ
D. Ⅰ、Ⅱ和Ⅲ