单项选择题
"gauge pressure" means（）.
A."vacuum" B."the excess of pressure above atmosphere" C."figure on a gauge" D.Any of the above
单项选择题 The （） is used to measure the volume of a liquid or gas through a pipeline within any given period of time.
单项选择题 Sacrificial zinc anodes are used on the saltwater side of diesel engine heat exchangers to（）.
单项选择题 With a （） load the voltage and current are in phase.
