（）的安装必须有坡度。
A.集气管
B.吸气管
C.II型管
D.桥管
参考答案：A, B
In relation to the sources of law in the Hong Kong Special Administrative Region:
(b) Explain the conditions necessary for the doctrine of precedent to operate. (6 marks)
什么是物体的弹性和塑性？
