单项选择题
Diesel engine ‘blow-by’ into the crankcase is caused by excessive ring（）
A.back clearance B.side clearance C.gap clearance D.taper clearance
单项选择题 Heavy residual fuel oils are heated prior to centrifuging to （）
单项选择题 In a diesel engine, blow-by is generally the result of worn（）
单项选择题 For optimum results, centrifugal purification of heavy fuel oil should be accomplished with the fuel at the lowest practicable（）
