单项选择题
In a radial piston pump, reversal and control of fluid flow are accomplished by moving the （）.
A.central valve B.radial plunger C.floating ring D.cylinder body
单项选择题 Increasing the moisture content of conditioned air is known as （）.
单项选择题 A reciprocating air compressor is running roughly and vibrating excessively, indicating that the （）.
单项选择题 The term "pour point" is defined as the lowest temperature at which lubricating oils will flow （）.
