天山-4-2

Q2:
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.

想不清楚为什么选b阿。

        i vote for C

        open to discussion

        高山地区每单位开采的成本高，平原地区每单位开采的成本低，以前一起开采，所以综合成本高于平原开采

        现在只开采平原地区，所以成本下降

        B是无关

http://forum.chasedream.com/dispbbs.asp?boardID=24&ID=86893&page=1

请看下这个帖子再发贴。 谢谢