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. Even after Balzania began requiring surface mine operators to pay reclamation
costs, coal mines in Balzania continued to be less expensive to operate than coal
mines in almost any other country.
B. 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.
C. 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.
D. Even after Balzania began requiring surface mine operators to pay reclamation
costs, surface mines continued to produce coal at a lower total cost than
underground mines.
E. As compared to twenty years ago, a greater percentage of the coal mined in
Balzania today comes from surface mines.
我选E，答案是C。不解...
把E中的greater改成smaller就对了!
文章说R是对surface mines收的,所以只要surface mines下降,其他mines不变就可以解释原因!!
所以C就是答案
不知LZ理解否?
howevr,the lower surface mines ,the lower average R cost?
??E
价格是跟需求有关系的吧。
c里面说，操作者早就已经减少了表面开采，那么收拾工作就很少 不需要再雇人来做了，所以价格就下降了。
我与2楼的有不同的意见。答案是c应该是对的，但是我对2楼的对E的解释不太同意。
由题意可以得出，average reclamation cost =总成本费用 / 从地表矿藏所挖出的总吨数，
E只说明总吨数增加，即分母变大，但没有说到总成本费用怎么变，因此我们不能判定average reclamation cost 的变化。
E中，在分母（总吨数）增加的情况下，只要分子（总成本费用）的增加的程度小于分母（总吨数）增加的程度，average reclamation cost 就能减小，一样可以说明题中的现象。
反之，如果分母减少，只要分子减少的程度大于分母，也可以解释题中的现象。
不知道这样分析对不，恳请赐教。
XDJM们说得好，说得秒，说得狗年汪汪叫。我的想法是这样的：
我不选C理由是：在题干中我们找不到任何关于除了surface mines,还有其它种mines。在答案D中我们看到了underground mines。但这能不能说明在Balzania这个地方有underground mines开采煤？
E中答案的a greater percentage of the coal 看你怎么理解。如果是在同等mined-out land下，有greater...那它就就解释了题目中出现的现象。
E错的原因是：原文要解释的是surface mine的reclamation cost现在比25前刚开始低。不涉及其它类型的MINE，只是surface mine. E说的surface mine 比例更大更小都无关。如果原文说的是Mine 的reclamation 费用，而且说明surface mine 的reclamation cost比其它类型的Mine低，则E为答案。
C说的是surface mine中，reclamation cost高的山区地带现在不搞了，高的都是reclamation cost 低的，当然费用就降低。故为答案。
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