Most people are aware that outdoor air pollution can damage their health, but many do not know that indoor air pollution can also have significant health effects. Environmental Protection Agency studies indicate that indoor levels of pollutants may be 2-5 times, and (47) 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 (48) .
There are many sources of indoor air pollution in any home. These include combustion sources such as oil, gas, coal, wood, and tobacco products; building materials and furnishings as (49) as deteriorated (变坏的) asbestos-containing (含有石棉成分的) insulation (绝缘材料), wet or damp carpet, and cabinetry or furniture made of certain pressed (50) products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling (51) and humidification devices; and outdoor sources such as radon (氡), pesticides, and outdoor air pollution.
Immediate effects may show up after a single exposure or (52) exposures. These include irritation (刺激，过敏) of the eyes, nose, and throat, headaches, dizziness, and (53) . Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply (54) the person’s exposure to the source of the pollution, if it can be identified.
The likelihood of immediate reactions to indoor air pollutants depends on several factors. Age and pre-existing medical conditions are two important influences. In other cases, whether a person (55) to a pollutant depends on individual sensitivity, which (56) tremendously from person to person.

• A) reactsF) systems K) plastic
• B) diverseG) immediately L) eliminating
• C) identicalH) wood M) occasionally
• D) fatigueI) varies N) repeated
• E) reducingJ) indoors O) includes