单项选择题
The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
A.dead band action B.neutral zone action C.range D.on-off action
单项选择题 Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.
单项选择题 If the head pressure of a reciprocating refrigeration compressor is excessive, （）.
单项选择题 A salinity indicator is used to determine the （）.
