1 . Directions: Complete the following passage by using the words in the box. Each word can only be used once. Note that there is one word more than you need
agree                 suffer             system            notice               through
dangerous        space            limited       absorbs            let out

For years scientist have been worried about the effects of air pollution on the earth’s natural conditions. Some believe the air inside many houses may be more     1     than the air outside. It may be one hundred times worse.

Indoor air pollution can cause a person to feel tired, to     2     eye-pain, headache and other problems. Some pollutants can cause breathing disorders, diseases of blood and even cancer. Most scientists     3     that every modern house has some kind of indoor pollution. People began to     4     the problem in the early 1970s, when it was that builders began making houses and offices which did not waste energy. To do this they built buildings that     5     the flow of air between inside and outside. They also began using man-made building materials. These materials are now known to     6     harmful gases. As the problem became more serious, scientists began searching for a way to deal with it. They discovered a natural pollution control     7     for building green plants. Scientist do not really know how plants control air pollution. They believe that a plant’s leaves take in the pollutants. In exchange the plant produces oxygen     8     its leaves and through its tiny organizations on its roots. Scientists suggest that all buildings should have one large plant or several small plants inside for every nine square meters of space. Studies of different plants show that each     9     different chemicals. So the most effective way to clean the air is to use different kinds of plants. Having green plants inside your house can make it a prettier and healthier place.