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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

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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’ve 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 or salty water leaking into roadbeds, which 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 (CMA), perhaps the most promising alternative, look practical. CMA costs $ 600 a ton and has minimal side effect. Some researchers believe the cost can be halved by making CMA from waste cheese whey (乳浆).
    While CMA and other alternatives are being researched, many cities and states are cutting back on their use of salt.
The writer implies that using salt to keep roads safe has all the following disadvantages but the fact that______.
选项 A、salt corrodes underground cables
B、salt pollutes the air
C、salt poisons streams and kills trees
D、salt damages roads and vehicles
答案B
解析 本题是一道判断是非题。问作者暗示用盐保持道路安全有诸多不利，以下哪个不是作者暗示的不利方面。根据文章第二段内容，最近，经济学家们计算了实际花费。据环保局估计，由食盐引起的路面损坏及车辆腐蚀每年损失30亿美元。这并不包括对地下电缆的损坏，这笔损失给各项费用支出增加了数亿美元；它也不包括盐水渗入路基所致的损失费用，盐水杀死绿色植被，并且污染河流。因此，本题的正确答案应是B“食盐污染空气”，在原文中作者没有提到。
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