两道解释题，求牛牛们解释！

melody1101 · 发表于 2012-4-14 23:27:14

1、Technoligical improvements and reduced equipment costs have made converting solar energy directly into electricity far more cost-efficient in the last decade. But the threshold of economic feasibility for solar power (that is, the price per barrel to which oil would have to rise in order for new solar power plants to be more economical than new oil-fired power plants) is not changed at thirty-six dollars.
解释the apparently surprising result
答案是：Technological changes have increased the efficiency of oil-fired power plants.

2、Twenty-five years ago, Donia put in place regulations requiring operators of surface mines to pay for the reclamation of mined-out land. After that, reclamation technology has not improved. But, the average reclamation cost for a surface coal mine being reclaimed today is only three 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.
解释the drop in reclamation costs
答案是：Mine operators have generally ceased surface mining in the mountainous areas of Donia because reclamation costs per ton of coal produced are particularly high for mines in such areas.

sdcar2010 · 发表于 2012-4-14 23:47:17

The meaning of "the threshold of economic viabilityfor solar power " is defined as "price per barrel to which oil would have to rise in order for new solar power plants to be more economical than new oil-firedpower plants."
In other words, the price of oil at which the power generated by the solar power plant is cheaper than that by oil-fired power plants.

This is a paradox question, for which you need to provide a clause to explain the discrepancy. C does that.
If both the oil-fired and solar-powered plants increase their efficiency, the threshold of economic viability for solar power remains unchanged.

melody1101 · 发表于 2012-4-23 22:21:20

谢谢，那第二道题怎么解释呢？

sdcar2010 · 发表于 2012-4-24 07:25:56

The second is just a math problem to calculate the average cost from the sum of all the qualifying members. Write down the equation and you will know why the correct answer it correctf. One way to reduce the average is to avoid the high cost ones, as what the correct answer choice points out.

两道解释题，求牛牛们解释！

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