单项选择题
A.reducing exhaust gas velocity
B.increasing the frequency of gas vibration
C.the use of long head pipes
D.the use of zinc electrodes
单项选择题 An indication of an overloaded main propulsion diesel engine is （）
单项选择题 The most practical way of detecting an overload in one cylinder of an operating large, low-speed ,main propulsion diesel engine is to （）
单项选择题 Diesel engine mufflers or silencers reduce the engine exhaust noise by （）