单项选择题 Fuels of different qualities may require advancing or retarding the injection timing, in addition to which if the injection timing is advanced when the engine is running at loads below the （）, then a saving in fuel can be achieved.

单项选择题 The plunger is machined to very fine tolerances, as is the matched（）in which it reciprocates.

单项选择题 It should be evident that the amount of fuel injected into the cylinder is dependent on the position of the helix relative to the （）.