单项选择题
Hydraulic pumps most commonly used in steering systems are of the （）.
A.lobe type B.screw type C.axial piston type D.volute type
单项选择题 When an auxiliary boiler is panting and emitting black smoke, you should （）.
单项选择题 Close the （）.
单项选择题 Which pump is the self-priming pump?（）
