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Twenty years ago, Balzania put in place regulations requiring operators of surface mines to pay for the reclamation of mined-out land. Since then, reclamation technology has not improved. Yet, the average reclamation cost for a surface coal mine being reclaimed today is only four dollars per ton of coal that the mine produced, less than half what it cost to reclaim surface mines in the years immediately after the regulations took effect.
Which of the following, if true, most helps to account for the drop in reclamation costs described? A. In the twenty years since the regulations took effect, the use of coal as a fuel has declined from the level it was at in the previous twenty years. B. Mine operators have generally ceased surface mining in the mountainous areas of Balzania because reclamation costs per ton of coal produced are particularly high for mines in such areas. 我选的第一个，答案是第二个。如果矿主停止采矿了，虽然征收的费少了，可开矿的人也少了呀，average并不见得就减少~第一个跟第二个的结果不是一样的吗？都是采煤的少了？ 请教NN们~
[此贴子已经被作者于2008-9-11 12:16:08编辑过] | 
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发表于 2008-9-11 12:16:00
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