-Mary has just broken up with her boyfriend.      

-_________? I don't want to fall in love with her.      [ ]

A. What if                            

B. What's wrong      

C. What about you                

D. What of it

A．烧断细线后，B、C和弹簧组成的系统动量守恒，且机械能守恒

B．烧断细线后，A、B分离瞬间A的动能是E/3

C．烧断细线，A、B分离瞬间，C的动能是E/3

D．烧断细线，A、B分离后，弹簧的弹性势能最大值是3E/4