The term waterlogging in paragraph 6 means that
A. logs are floating in water
B. water is not available
C. the soil holds too much water
D. salts are removed from water
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Which of the following statements can be inferred from paragraph 1 about the history of communication？
A. Certain advances in technology have greatly changed communication．
B. People have both loved and feared new developments in technology．
C. We do not know what people thought about before modern technology．
D. The history of modern communication began in the fifteenth century．
The word each in paragraph 4 refers to
A. experiment
B. child
C. age
D. row
How are waterlogging and salinization related？
A. Salinization occurs only where waterlogging is a problem．
B. Waterlogging raises and concentrates salts near the surface．
C. Farmers add salts to irrigation water as a way to fertilize soil．
D. Both waterlogging and salinization contribute to soil erosion．
Why does the author mention corn and wheat yields in paragraph 7？
A. To illustrate the effect of a small amount of erosion
B. To explain why erosion affects only certain crops
C. To describe the result of a shift from traditional practices
D. To show how poor management influences crop yields
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