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⑺The ____ are busy fishing in the lake. (fish)
⑻The shoes are ____  to wear, I will not buy them. (comfortable )
⑼Help ____ to some meat, boys and girls. (you)
⑽You had better____  at home until it stops raining. (stay)