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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【B2】______ that indoor levels of pollutants may be 2 to 5 times, and【B3】______ more than 100 times, higher than outdoor levels. These levels of indoor air pollutants may be of particular【B4】______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【B5】______ soon after exposure or, possibly, years later. Immediate effects may show up after a single exposure or【B6】______ exposures. These include headaches, dizziness,【B7】______, and irritation(疼痛)of the eyes, nose, and throat. Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply【B8】______ the person’s exposure to the source of the pollution, if it can be identified.【B9】______. Age and preexisting medical conditions are two important influences.
    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.【B10】______. If the symptoms fade or go away when a person is away from home,【B11】______
【B3】
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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