单项选择题
The delivery rate of a variable stroke axial piston hydraulic pump is controlled by varying the position of the （）.
A.slide block B.tilting box C.pintle D.reaction ring
单项选择题 Which of the following statements describes the relationship between viscosity and specific gravity?（）
单项选择题 Some chloronated flourocarbon refrigerants may decompose into a toxic irritating gas if it is （）.
单项选择题 A refrigeration system contaminated with moisture can be affected by （）.
