单项选择题
For optimum results, centrifugal purification of heavy fuel oil should be accomplished with the fuel at the lowest practicable（）
A.throughput B.additive percent C.cetane number D.TBN number
单项选择题 Diesel engine piston ring blow-by is usually caused by excessive ring clearance at the ring（）
单项选择题 In a four-cycle diesel engine piston blow-by can result in increased（）
单项选择题 The most effective method in removing water from diesel fuel oil is by（）
