单项选择题
A.too low starting air pressure
B.main start valve closed
C.neither A nor B
D.A and B
单项选择题 Which of the following is true about the fuel injection with an ordinary diesel engine?（）
单项选择题 Which of the following is a factor of fuel oil almost having nothing to do with the formation of combustion products?（）
单项选择题 Which of the following firing order may be used for an 6 cylinder engine?（）