绘图题：画出浮动床本体管伐示意图。
参考答案：
Oligopolists have an incentive to cheat on collusive agreements in order to:（）
A. avoid competitive practices.
B. restrain trade and hinder trade relationships.
C. increase their individual share of the joint profit.
下列变化中，属于物理变化的是（ ）
A．煤的干馏
B．石油的分馏
C．石油的裂化
D．铝热反应
