题目内容：

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 3～5 times，and occasionally 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.

There are many sources of indoor air pollution in any home.These include sources such as oil，gas，coal，wood，and tobacco products，building materials，wet or damp carpet，and furniture made of certain pressed wood products，products for household cleaning and maintenance，personal care，or hobbies，central heating and cooling systems.

Immediate effects may show up after a single exposure (暴露) or repeated exposures.These include irritation of the eyes，nose，and throat，headaches，dizziness.Such immediate effects are usually short­term and treatable.Sometimes the treatment is simply removing 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 pre­existing medical conditions are two important influences.In other cases，whether a person reacts to a pollutant depends on individual sensitivity，which varies tremendously from person to person.Some people can become sensitized to biological pollutants after repeated exposures，and it appears that some people can become sensitized to chemical pollutants as well.

Certain immediate effects are similar to those from colds or other viral (病毒性的) diseases，so it is often difficult to determine if the symptoms are a result of exposure to indoor air pollution.While pollutants commonly found in indoor air are responsible for many harmful effects，there is considerable uncertainty about what concentrations or periods of exposure are necessary to produce specific health problems.People also react very differently to exposure to indoor air pollutants.Therefore，further research is needed to better understand the effects of indoor air pollution and to find efficient ways to protect our health.

1.According to the first paragraph，which of the following is NOT true?

A．People often fail to notice indoor air pollution.

B．Indoor air pollution sometimes is more dangerous than outdoor air pollution.

C．Outdoor air pollution may not be so serious as indoor air pollution.

D．It is obvious that people have been paying more attention to indoor air pollution.

2.According to the author，which may NOT be the source of indoor air pollution?

A．Building materials.  B．Wet carpet.

C．Cooling system.  D．Refrigerators.

3. What does the underlined word “irritation” in the third paragraph probably mean?

A．Bad intention.  B．Much sensitivity.

C．Injury.  D．Carelessness.

4. Which of the following might be the best title for the passage?

A．Reactions of Pollution  B．Danger from Home

C．Pollution Resources  D．Different Pollutions