单项选择题
Which of the following firing order may be used for an 6 cylinder engine?（）
A.1-2-3-4-5-6 B.1-2-3-6-5-4 C.1-5-3-6-2-4 D.1-3-4-5-6-2
单项选择题 Which of the following can be obtained by means of an indicator card?（）
单项选择题 Which of the following can be directly obtained by means of an indicator card?（）
单项选择题 Which factor of the following affects not only the fuels combustion but also the engine’s maintenance?（）
