--People should use public transport instead of their own private cars.

--- _______.The roads are too crowded as it is.

A．Eventually

B．Exactly.

C．Particularly

D．Actually.

短期平均成本曲线呈U形的原因与( )。

A．规模报酬有关

B．外部经济与不经济有关

C．生产要素的边际报酬有关

D．固定成本与可变成本所占的比重有关