单项选择题
Sediment collects in a tubular purifier （）.
A.on top cover B.on sides of bowl C.in drain line on the discs D.on the discs
单项选择题 Sea water is not used directly as a coolant because of （）.
单项选择题 Sea water is not directly used as a coolant for engines because of its （）.
单项选择题 "Scavenging" on a diesel engine means （）.
