设有关系R(S，D，M)，其函数依赖集F={S→D，D→M}，则关系R至多满足( )。

A．Ⅰ和Ⅱ
B．Ⅰ、Ⅱ和Ⅲ
C．Ⅲ和Ⅳ
D．Ⅰ、Ⅱ、Ⅲ和Ⅳ

A．SELECT sno FROM sc WHERE cno="c1"AND cno="c2"
B．SELECT sno FROM sc WHERE cno="cl'，AND SELECT sno FROM sc WHERE cno="c2"
C．SELECT sno FROM sc WHERE cno="cl" UNION SELECT sno FROM sc WHER：E cno="c2"
D．SELECT sno FROM sc WHERE cno="cl"AND sno IN(SELECT sno FROM sc WHERE cno="c2")