2、四个选项（A,B,C和D）中，选出最佳选项，并在答题纸上将该项涂黑。AForyearsscientistshavebeenworriedabouttheeffectsofairpollutionontheearth’snaturalconditions.Somebelievetheairinsidemanyhousesmaybemoredangerousthantheairoutside.Itmaybeonehundredtimesworse.Indoor air pollution can cause a person to feel tired, to suffer eye p
3、ain, headache and other problems. Some pollutants(污染物) can cause breathing disorders,diseases of blood and even cancer. Most scientists agree that every modern house has some kind of indoor pollution.People have paid more attention to the problem now. It is true that when builders began making
4、houses and offices they did not waste energy. To do this they build buildings that limited the flow of airbetween inside and outside. They also began using man-made building materials. These materials are now known to let out harmful gases.As the problem became more serious, scientists began s
5、earching for a way to deal with it. They discovered a natural pollution control system for building--green plants. Scientists do not -14-really know how plants control air pollution. They believe that a plant’s leaves absorb or take in the pollutants. In exchange the plant lets out oxygen thro
6、ugh its leaves and tiny organizations on its roots. Scientists suggest that all buildings should have one large plant or several smallplantsinside for every nine square meters of space. Studies of different plants show that eachabsorbs different chemicals. So the most effective way to clean th
7、e air is to use different kinds of plants. Having green plants inside your house can make it a prettier and healthier place.1.Generally speaking, indoor air pollution may be more harmful than the air outside because________.A. indoor ai
