单项选择题
The delivery rate of an axial-piston hydraulic pump is controlled by varying the position of the （）.
A.sliding block B.pintle C.reaction ring D.tilting box or swash plate
单项选择题 Badly leaking refrigeration compressor discharge valves will cause（）.
单项选择题 Mechanical energy in transition is referred to as （）.
单项选择题 If you change from a low pour point lubricant to a high pour point lubricant in a refrigeration system, （）.
