下列有关命题的说法正确的是 (     )．

A：命题“若，则”的否命题为：“若，则”．

B：“” 是“”的必要不充分条件.

C：命题“若，则5 a blue sweater and white shoes. He is Jim. He is 6 American student. He is 14. He 7 his school very much. The girl is Jim's sister, 8 name is Cindy. She is 11. She is in a yellow dress. Her shoes are yellow. 9 . Now they are standing here, they are waiting for their friends. They 10 to play games under the tree.