—Tom hasn't paid for the things he bought, has he?            

—           . His father will.pay for him.          [ ]

A. Yes, he has                      

B. Yes, he did          

C. No, he hasn't                    

D. No, he didn't

a表示胶头滴管中的液体，b表示烧瓶中的气体。不能形成喷泉实验现象的a中液体和b中气体的组合是（   ）

A．a—NaOH溶液、b—HCl气体

B．a—NaOH溶液、b—CO₂气体

C．a—HCl溶液、b—NH₃气体

D．a—水、 b—CO₂气体