单项选择题
A viscosity regulator used for an engine is usually provided in order to （） for an engine burning heavy fuel oil.
A.regulate the fuel supply B.maintain a constant fuel viscosity at the fuel valves C.maintain efficient cooling D.alter the fuel density
单项选择题 A manometer is used to measure （）.
单项选择题 "gauge pressure" means（）.
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.
