单项选择题 Too much excess air is （）because the heat generated is being lost through the exhaust trunking instead of being made used of in heating the water to produce steam.

单项选择题 （） the oxygen content in the exhaust gas, （） the combustion is.

单项选择题 Injectors on modern engines are cooled by a combination of the intensive bore cooling in the cylinder by a combination of the intensive bore pockets and by the fuel which is re-circulated through the injector when the follower is on the （）of the cam or when the engine is stopped.