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  3. At noon on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts p

At noon on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts p

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问题     At noon on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts per million (ppm). The average for the day was 399.73 and researchers at the observatory expect this figure, too, to exceed 400 in the next few days. The last time such values prevailed on Earth was in the Pliocene epoch (上新世) 4m years ago, when jungles covered northern Canada.
    There have already been a few readings above 400 ppm elsewhere—those taken over the Arctic Ocean in May 2012, for example—but they were exceptional. Mauna Loa is the benchmark (标准) for CO2 measurement because Hawaii is so far from large concentrations of humanity. The Arctic, by contrast, gets a lot of polluted air from Europe and North America.
    The concentration of CO2 peaks in May, falls until October as plant growth in the northern hemisphere’s summer absorbs the gas, and then goes up again during winter and spring. This year the average reading for the whole month will probably also reach 400 ppm, according to Pieter Tans, who is in charge of monitoring at Mauna Loa, and the seasonally adjusted annual figure will reach 400 ppm in the spring of 2014 or 2015.
    Mauna Loa’s readings are one of the world’s longest-running measurement series. The first, made in March 1958, was 315 ppm. That means they have risen by a quarter in 55 years. In the early 1960s they were going up by 0.7 ppm a year. The rate of increase is now 2.1 ppm—three times as fast—reflecting the relentless rise in green-house-gas emissions.
    As a rule of thumb, CO2 concentrations will have to be restricted to about 450 ppm if global warming is to be kept below 2 degrees. Because CO2 stays in the atmosphere for decades, artificial emissions of the gas would have to be cut immediately, and then fall to zero by 2075, in order to achieve 450 ppm. There seems no chance of that. Emissions are still going up. At current rates, the Mauna Loa reading will rise above 450 ppm in 2037.
Which is true according to the last paragraph?
选项 A、CO2 remains in the atmosphere for several dozen years.
B、At current rates, Mauna Loa reading will rise above 450 ppm by 2075.
C、The chance of cutting emissions and achieving 450 ppm by 2075 is good.
D、Human’s gas emissions have been cut at once in order to achieve 450 ppm.
答案A
解析 A项对应原文：Because CO2 stays in the atmosphere for decades... 其中“stays”=“remains”：“decades”=“several dozen years”，故选项A正确。B项对应原文：At current rates, the Mauna Loa reading will rise above 450 ppm in 2037. 原文提到的是2037年，而非2075年，故选项B错误。C项对应原文：...artificial emissions of the gas would have to be cut immediately, and then fall to zero by 2075, in order to achieve 450 ppm. There seems no chance of that. 原文说的是“no chance”，该选项说的是“the chance…is good”，故错误。D项也对应以上原文。原文说的是“have to be cut”，而不是“have been cut”，故选项D错误。答案为选项A。
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