单项选择题
Sea water is not directly used as a coolant for engines because of its （）.
A.low specific heat B.corrosive action C.high expense D.acid property
单项选择题 "Scavenging" on a diesel engine means （）.
单项选择题 Scavenging is （） of exhaust gases by blowing in fresh air.
单项选择题 Rotating flyweights acting against spring pressure make a simple type of （）.
