单项选择题 If the needle valve in a fuel injection nozzle sticks open （）.

单项选择题 If the flame from combustion in the cylinder of a four-stroke engine past the piston into the space below, the accumulation of flammable mixture would be ignited, thus resulting in （）.

单项选择题 If the engine does start on air, but combustion does not immediately begin, the cause may not be （）.