单项选择题
The knock occurring when a cold diesel engine is started and continues while running at low speed, but stops when the engine reaches normal operating speed and temperature, is（）.
A.caused by retarded injection timing B.caused by a mechanical defect in one cylinder C.caused by high fuel injection pressures D.normal for these conditions
单项选择题 Failure to open the diesel engine test cocks after a long period of shutdown, prior to starting may result in （）
单项选择题 Heat damage to fuel injection nozzles can be prevented by avoiding （）
单项选择题 Critical speed in diesel engines occurs when engine torque pulsations become （）
