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.
风速和风向会影响放射性尘粒到达的时间；冰雹则能带出空气中的放射性尘降物。
Wind speed and direction will affect arrival time of fallout; precipitation may wash fallout from the atmosphere.
微小的固体和液体粒子——一些你能够看到，一些你看不到的——在每年的任何时间，在星球中的任何一处空气中都能够被发现。
Tiny solid and liquid particles-some you can see, some you cannot-can be found in the air everywhere on the planet, at any time of year.
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