?1. by air 乘飛機(jī)。如：He went to Paris by air. 他乘飛機(jī)去了巴黎。Which is faster, by air or by train? 坐飛機(jī)快還是坐火車快? 2. air 在空中；在流傳中；渺茫。如：Birds fly in the air. 鳥在空中飛。The plan is quite (up) in the air. 計(jì)劃還相當(dāng)渺茫。3. on the air . 在廣播中。如：I heard the news on the air. 我在廣播中聽到了這條消息。What’s on the air this evening? 今晚有什么廣播節(jié)目?