当边际收益递减时，总变动成本将：
   A．按递增的速度递减
   B．按递增的速度递增
   C．按递减的速度递减
   D．按递减的速度递增

A．America is now the only developed country without the policy.
B．It has now become a hot topic in the United States.
C．It came as a surprise when Australia adopted the policy.
D．Its meaning was clarified when it was established in Australia.

A.总成本等于总变动成本
B.总成本大于总变动成本
C.总成本是否大于总变动成本不确定
D.平均变动成本的最低点恰好在总成本曲线的拐点上