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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.
CMA is being researched because it is thought to______.
选项 A、be the only choice
B、have less side effect
C、be cheaper than other alternatives
D、be made from cheese whey
答案B
解析 本题是一道具体细节题。问人们正在研究CMA的原因是什么。利用查阅式阅读法，我们可以在文章的第三段后半部分找到相关信息。这部分指出，由于食盐的使用所带来的一系列费用，人们便开始改用钙镁醋酸盐(CMA)，也许钙镁醋酸盐是最有开发前途的替代品，而且也很实用。每吨CMA价值600美元，副作用最小。科研人员相信，用废干酪乳浆制取CMA可使费用减半。因此，本题的正确答案是B“使用CMA的副作用更少”。
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