在这段时间里，自然中鸟类的食物越来越少，空气温度也越来越低，额外的喂养可以让鸟类保持温暖和健康。
During this time when fewer natural foods are available and air temperatures are lower, extra feeding can keep a bird warm and well.
现代高技术战争中，人员直接暴露于外界空气中的机会越来越少，大多数时候都处于各种作战及运输装备的舱室内。
In modern high technical wars, there is less and less opportunity for personnel directly exposing to exoteric air, they are usually disposed in cabins of various campaign and transport equipment.
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