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mardi 17 janvier 2012

Acid Rain

Acid rain is a form of pollution. It can occur naturally near volcanoes or some wetlands. But the main cause of acid rain is from human sources, such as power plants, factories and motor vehicles. Factories produce many kinds of toxic chemicals. Among them, the key substances of acid rain are 502(sulfur dioxide) and NO(nitrogen oxide).
When 502 and NO are emitted into the atmosphere in factory smoke, they get absorbed by water droplets in the clouds. The chemicals change the water's pH level by turning them to acid. Later, when the toxic water droplets fall to the earth as rain, snow or mist, the acid rain has adverse impacts on the environment.

When the acid rain falls to the earth, it changes the pH of the soil into lower levels. So the soil activates toxins and takes away essential nutrients and minerals. It stops the growth of the plant. Also, the growth of trees is slowed, and the leaves and needles of them turn brown and die. The death of trees is not usually a direct result of acid rain, but it weakens trees and makes them more susceptible to other threats. Very strong acid rain can even dissolve building materials. Although direct harm to human health has not been proved, some scientists have claimed it causes illness and premature deaths. Nowadays, many people try to safeguard the environment from acid rain.
power plant        a building where electricity is produced to supply a large area
1.  According to paragraph 1, which of the following is true?
    a. Acid rain is mostly caused by humans.    b. Wetlands and volcanoes pollute the rain.
    c.  Acid rain usually comes from volcanoes.     d. Pollution from rivers and oceans makes acid.
2. It is indicated in paragraph 2 that
    a. toxic chemicals are always harmful.    b. the chemicals turn water droplets into acid.
    c. snow and mist can make acid rain.    d. the chemicals are absorbed by pollution.
3. It is NOT stated in paragraph 3 that acid rain
    a. changes soil pH into the low level    b. stops the growth of the plant
    c. turns rivers into strong acid        d. can be connected with the disease of trees
4. All of the following are true EXCEPT that acid rain
    a. can fall as snow        b. has terrible effects
    c. falls in a small area         d. can dissolve buildings

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