Which of the following best describes the overall organization of the passage

A．The author describes a concept by analyzing its three forms,

B．The author compares and contrasts two types of human relations.

C．The author presents the points of view of three experts on the same topic.

D．The author provides a number of concrete examples and then draws a conclusion.

油缸由（）、缸座、缸筒、缸套、连接体、连接螺栓和密封圈等组成.

A.推板

B.活塞杆

C.垫管

D.推板