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  3. Most people are aware that outdoor air pollution can damage their health, but many do not know that indoor air pollution also ca

Most people are aware that outdoor air pollution can damage their health, but many do not know that indoor air pollution also ca

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问题     Most people are aware that outdoor air pollution can damage their health, but many do not know that indoor air pollution also can cause【B1】______health effects. U.S. Environmental Protection Agency studies of human exposure to air pollutants indicate that indoor levels of pollutants may be 2 to 5 times, and【B2】______more than 100 times, higher than outdoor levels. These levels of indoor air pollutants may be of particular concern because most people spend about 90% of their time indoors.
    Many sources of indoor air pollution can be found in any home or office. Health effects from indoor air pollutants may be【B3】______soon after exposure or, possibly, years later. Immediate effects may【B4】______after a single exposure or repeated exposures. These include headaches, dizziness,【B5】______, and irritation(疼痛)of the eyes, nose, and throat. Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply【B6】______the person’s exposure to the source of the pollution, if it can be identified. The likelihood of immediate reactions to indoor air pollutants【B7】______several factors. Age and preexisting medical conditions are two important【B8】______.
    Certain immediate effects are similar to those from colds or other diseases, so it is often difficult to determine if the symptoms are a result of exposure to indoor air pollution For this reason, it is important to【B9】______the time and place symptoms occur. If the symptoms【B10】______ or go away when a person is away from home, for example, an effort should be made to identify indoor air pollutant sources that may be possible causes.
【B2】
选项
答案occasionally
解析 若去除此空，并不影响句子大意，故推断空格处应填入虚词。occasionally意为“有时候”，拼写时要注意双写c和l。
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