单项选择题
All of the following steps are taken in starting a centrifugal pump，EXCEPT to（）.
A.set the relief valve B.check the lubrication system C.vent the pump casing D.open the pump suction and discharge valves
单项选择题 After an engine is started you should（）.
单项选择题 A wobbling tail shaft is an indication of（）.
