单项选择题
A.contraction B.retraction C.expansion D.shrinkage
Among the basic categories of equipment, which of the f...
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
In a general cargo crane, （） is fitted to raise or lowe...
单项选择题In a general cargo crane, （） is fitted to raise or lower the jib.
A.the slewing motor B.the luffing motor C.the hoisting motor D.none of the above
External and internal leakage in hydraulic systems may ...
单项选择题External and internal leakage in hydraulic systems may be caused by （）.
A.unusual vibration B.excessive worn parts C.abnormal pressure D.any of the above
