第五天的最后一个段子讲geology的
If you flew over certain parts of Nebraska and Texas by plane, you might notice some large areas appearing as bright green circles many hundreds of feet across. This green is unusual in the high plains area where the climate is very dry. These green patches are the result of a new technique for mining the underground water. In this technique , miners bore deep holes in the ground until they reacha special geological formation called an [ocheropher]. The water which has collected in this ocherophers for hundreds of years is called fossil water or ground water. It is pumped up through the bored hole and spray over the land to irrigate the crops. Raising crops such as cotton and wheat watered in this way creates the fertile green areas that contrasts vividly with the natural brown of the plains. Crop yields have increased dramatically . However they've created a serious environmental problem. The problem is that the water is being removed from many ocherophers faster than it can be replenished naturally. Ground water levels have dropped rapidly and it's becoming more difficult and expensive to get this water. In some parts of Texas , water levels in some of the ocherophers have declined by more than four hundred feet in twenty-five years. This process of using water faster than it can be replaced is wide-spread and serious. 每日托福训练5天.rar (2.79 MB)
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