单项选择题
Among the basic categories of equipment, which of the following are used to allow the hydraulic energy to be controlled?（）
A.hydraulic pumps B.valves C.hydraulic cylinders D.hydraulic motors
单项选择题 （） are used for cargo handling.
单项选择题 In a hydraulic system, （） are used to protect the system from over pressure.
单项选择题 A hydraulic motor may be driven by （）.
