单项选择题 The interior of some diesel engine saltwater heat exchangers are protected from corrosion by the use of（）

单项选择题 Proper lubrication of the main bearing is more easily obtained in a single acting four-stroke/cycle diesel engine than in a single acting two-stroke/cycle diesel engine because （）

单项选择题 Which of the fuel injection systems listed uses a spring loaded differential spray needle valve and individual pump for each cylinder?（）