有如下的SOL语句：
Ⅰ．SELECT sname FROM s，sc WHERE grade＜60
Ⅱ．SELECT sname FROMs 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)，
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