单项选择题 For a fire to begin there must be present a combustible material, oxygen or air to （）combustion, and a source of heat at a temperature high enough to start combustion.

单项选择题 Start the turning gear, and with some one hand-operating the cylinder lubricators at regular intervals, and with the indicator cocks （）, and with the control gear in the （）position, give the engine at least one complete turn.

单项选择题 If the engine can be started and maneuvered on high viscosity fuel, the （）of the fuel reaching the injectors should be raised to such a point that the viscosity is less than the required value, ie27c St.