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  3. In an average winter, highway departments spread some ten million tons of salt to keep roads safe. The corrosive effects are wel

In an average winter, highway departments spread some ten million tons of salt to keep roads safe. The corrosive effects are wel

admin2009-06-15  102
问题 In an average winter, highway departments spread some ten million tons of salt to keep roads safe. The corrosive effects are well known, but for years they’ re been dismissed with the argument that at around $ 25 a ton, salt is far cheaper than any alternative.
   Lately, economists have added up the actual costs. The Environmental Protection Agency estimates that salt-induced road damage and vehicle corrosion cost $ 3 billion a year. That does not include damage to underground cables, which adds hundreds of millions to utility bills. Nor does it reflect the cost of brine leaking into porous water pipes, threatening the water supply. Salty water leaches into roadbeds, kills evergreens and poisons streams.
   The various costs probably add another $ 2 billion to the national salt bill. Scientists estimate the full economic, or "life cycle," cost for a ton of salt at $ 500, or 20 times the $ 25 purchase price. That begins to make the switch to calcium magnesium acetate, perhaps the most promising alternative look practical. CMA, made from acetic acid and dolomitic(含白石的) lime, costs $ 600 a ton and has minimal adverse effect. Some researchers believe the cost can be halved by making CMA from waste cheese whey or pulp-mill effluent.
   While CMA and other alternatives are being researched, many cities and states are cutting back on their use of salt. Keeping dispensing equipment in good repair helps reduce the amount spread.
选项 A、road damage
B、vehicle corrosion
C、damage of underground cables
D、car accident
答案D
解析 第一段第一句即点明冬天在路上撒盐是为了防止发生车祸。但盐可产生许多副作用，例如腐蚀街道和车辆，毁坏地下管道，威胁水供给等，这些也就是前三项的内容，所以选D。
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