Soil can be acidic,neutral,or basic. The pH of the soil is determined by the nature of the rock from which it was formed,and by the nature of the plants that grow and rot in it.
The acidity of rain and snow can lower the pH of the groundwater that enters the soil. By burning fossil fuels such as coal,oil and gasoline,humans have been contributing to higher levels of acidity in many soils. When fossil fuels are burned,gases are released into the air and then fall back to earth as acid rain. Acid soil increases the problem of carrying nutrients to lower soil levels. As nutrients are removed,soil is less fertile. Plants grow more slowly in acidic soil,and also become easily attacked by diseases.
1. The layer of soil that provides necessary nutrients for plant growth is called .
A. litterB. topsoilC. humusD. subsoil
2. According to the text,which of the following isNOT true?
A. Soil forms from weathered rock on the earth surface.
B. The deeper layer of soil is darker in colour than the surface soil.
C. Air pollution is partially responsible for acid soil.
D. Groundwater tends to carry away nutrients for plant growth.
3. We can infer from the passage that the water table lies .
A. between the topsoil layer and the subsoil layer
B. in the subsoil layer above bedrock
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