单项选择题 The fresh air coming in through the inner air ports, is compressed by（） to a higher pressure.

单项选择题 The fourth engineer accompanied by the workers on oil barge measures the oil levels, temperature and （） in the tanks.

单项选择题 The four-stroke engine is used for （） and sometimes for main propulsion with a gearbox to provide a propeller speed of between 90 to 120 rev/min.