单项选择题
Diesel engine piston ring blow-by is usually caused by excessive ring clearance at the ring（）
A.back B.side C.gap D.bottom
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（）
单项选择题 On board supply vessels, a centrifuge is normally used to purify（）
