单项选择题
The usual number of single-acting pistons used in a variable stroke axial-piston pump is （）.
A.3 or 5 B.5 or 7 C.7 or 9 D.9 or 11
单项选择题 The heat identified by only a change in temperature is known as （）.
单项选择题 The static suction lift of a pump is the difference in elevation between the （）.
单项选择题 The sum of the sensible heat and the latent heat of any substance is known as （）.
