the main dining-room was filled with people eating and drinking with the
^^^
assured, complacent air of seasoned sailors.
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这里air可以解释为氛围 气氛
air相关的意思还有这么几种 a: outward appearance of a thing 如an air of luxury b: a surrounding or pervading influence : atmosphere 如 an air of mystery c: the look, appearance, or bearing of a person especially as expressive of some personal quality or emotion : demeanor 如an air of dignity d: an artificial or affected manner 如 put on airs