Before central air conditioning systems, it was common for people to open their windows to circulate air through their homes when the weather was mild.
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\r\nOpened windows naturally ventilate the air inside the house, replacing stale, stuffy indoor air with fresh outdoor air. The drawback, however, is that open windows also allow pollen, dust, moisture, and other pollutants into the home. 

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在中央空调系统出现之前，人们通bob国际娱乐常在天气温和的时候打开窗户让空气流通。

打开的窗户自然地使室内空气流通，新鲜的室外空气取代了污浊、闷热的室内空气。然而，缺点是开着的窗户也会让花粉、灰尘、水分和其他污染物进入室内。