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Newspapers often tell us of floods in some parts of the United States.
Nearly every year on the great central drainages heavy rains and melting snow cause the waters to pour out the mountains and plains, to turn brooks into torrents, and to swell quiet streams into wild uncontrolled rivers. From Cairo to New Orleans, and from Pittsburgh to Paducah, the cry "River rising!" is a familiar yet fearful voice. . . When the rivers sometimes become too high or too swift to be controlled communities are flooded, families flee from their homes, croplands are washed out, and transportation comes to a halt. Hunger, disease, and death follow the wild waters.
Although given less publicity, the agricultural damage done by the many smaller, more frequent floods usually far exceeds the losses caused by the very grand ones. In the Central States, ditches and drains cause the flows from spring rains and melting snow to run far more rapidly than in the days before white men settled on the land. Once, excess spring flood waters emptied into lakes and swampy lands, there to be detained for slow release into stream and rivers. Now, systematic drainage has actually eliminated these natural reservoirs.
In the more rolling sections of the East, spring runoff was formerly absorbed and held temporarily in the porous soils beneath the unbroken expanse of forest. When large areas were converted to farm use, removal of the forest and the practice of up-and-down hill plowing deprived the soils of much of their ability to catch and store water.
The effects of eliminating the natural forest cover are shown in the gullied farm lands and widened stream channels found in some densely settled areas. Partly because the stream channels are more or less filled with material washed down from the uplands, and partly because storm runoff has increased, the channels are today no longer able to carry all the flow from heavy rains. This explains why the streams overtop banks far more often than in the days before settlement.
26. The best title for the selection would be______.
A. River Rising! River Rising! B. Forests and Floods
C. Flooding in the U. S. D. The Results of Flooding
27. All of the following cause floods EXCEPT______.
A. heavy rain B. melting snow
C. increasing storm runoff D. porous soil
28. The author states that______.
A. lakes and swamps once acted like natural reservoirs
B. up-and-down hill plowing catches and stores water
C. stream channels are the best carriers of water
D. floods are easily prevented and controlled
29. According to the selection, streams overtop their banks partly because______.
A. material from higher land is washed into them
B. ditches and drains lead into them
C. rivers become too swift
D. snow melts more rapidly nowadays
30. The floods which are given most publicity______.
A. cause no damage
B. cause the most damage
C. cause less agricultural damage than the many smaller, more frequent floods
D. far exceed the smaller, more frequent floods in agricultural loss
26. C 27. D 28. A 29. A 30. C |
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发表于 2016-7-11 18:39:40