单项选择题
A.total head
B.discharge head
C.net positive suction head
D.suction head
单项选择题 The delivery rate of a variable stroke axial piston hydraulic pump is controlled by varying the position of the （）.
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 （）.