— Let's bet on Tom's performance in the coming examination; the loser has to treat the other

       to a dinner.   

— ______________. [ ]

A. I'm afraid so     

B. You've got a point  

C. It's a deal

D. You are welcome

如图甲、乙是同学们做过的两个物理实验。

甲的现象：“从B管右端向管内吹气，A管水面上升”；说明的原理是                   ，

乙的现象：“迅速击打硬纸板，鸡蛋不会随硬纸板飞出”；说明的原理是                    。