单项选择题
In an electro-hydraulic steering gear system, when will the variable displacement pump be placed on stroke?（）
A.When the helm is at any angle other than amidships B.When the six-way valve is opened C.When the ram relief valves lift D.When the redder angle is different from the position of the helm
单项选择题 An additive used to improve the ability of a lube oil to reduce friction is known as a/an （）.
单项选择题 The suction - force principle of operation is a typical characteristic of （）.
单项选择题 Air leakage between the shaft and stuffing box packing in a centrifugal pump is prevented by （）.
