单项选择题
Among the basic categories of equipment, which of the following are used to convert the hydraulic energy into linear motion?（）
A.Hydraulic pumps B.Valves C.Hydraulic cylinders D.Hydraulic motors
单项选择题 In a general cargo crane, （） is fitted to raise or lower the jib.
单项选择题 External and internal leakage in hydraulic systems may be caused by （）.
单项选择题 What type of valve is used to direct the flow of hydraulic fluid?（）
