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.
【B4】

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答案show up

解析 根据空格前的情态动词may判断这里应填入原形动词。show up的意思是“出现”。
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