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  3. Every 101 minutes or so, a Department of Defense imaging satellite circles the Earth, capturing images from the equator to the p

Every 101 minutes or so, a Department of Defense imaging satellite circles the Earth, capturing images from the equator to the p

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问题     Every 101 minutes or so, a Department of Defense imaging satellite circles the Earth, capturing images from the equator to the polar ice caps. It’s that DOD drone(colorfully named the DMSPF-17)that monitors geologic changes, such as the decreasing size of the Arctic and Antarctic ice covers. The images it snaps are the ones most people see of the Earth’s two white domes, which have been steadily diminishing for the past decade.
    Skimming over the top of the world feels a bit like being on a different planet, according to Rick Steiner, a marine conservation researcher at the University of Alaska. For the past two years, Steiner has led research missions flying low over thousands of miles of Arctic seas for a handful of polar climate scientists, some of whom work for the federal government. He times the daylong voyage to coincide with the time of year when sea ice is at a minimum, the exact end of summer melting in mid-September, before the autumn cool begins to refreeze some of the water. Having lived in Alaska for 30 years, Steiner can tell you in personal detail how the minimum has shrunk from year to year. He calls the voyage his annual "bearing witness to the Arctic crisis" trip.
    The crisis has been mapped out in precise detail in slide shows and research papers, with startling statistics. The past three summers have seen the lowest ice volume ever recorded, according to data released annually by the National Snow and Ice Data Center(NSIDC). The sea-ice minimum in 2007(1.6 million square miles)was the single lowest year, with nearly 40 percent less ice than the seasonal average recorded over the past three decades. And the problem is only expected to worsen. As the ice melts, it releases highly concentrated carbon and methane(甲烷)that is locked in the permafrost(永冻层), creating an accelerating warming loop. An additional compounding factor is that dark oceans absorb more of the sun’s energy than light-colored ice, which reflects a large portion of it. That means that the more ice melts over the summer, the more open ocean there is, which leads to more absorbed energy and warmer oceans, which means that less ice forms the following winter, which leads to even more open ocean the following year. Early this past summer, researchers thought 2009 would be even worse than 2007 in terms of melting, until a late-arriving wind from the equator brought cool air that prevented even more melting.
    "When you’re actually looking out the window and seeing mile after mile of warm ocean water where there used to be sea ice that you once walked around on, it gives you the certainty that something major is going on there," says James Overland, a marine environmental researcher with the National Oceanic and Atmospheric Administration. The thickness of the ice and water temperatures—which were also measured at disturbingly high levels by Steiner and his team this year—are also measurements you can’t make by peering at satellite images.
What is the main idea of the passage?
选项 A、Ice covers have been diminishing for the past decade.
B、It is DOD drone that monitors geologic changes.
C、Steiner’s annual voyages bear witness to the Arctic crisis.
D、Ice-melting is creating an accelerating warming loop.
答案D
解析 主旨题。作者在这篇文章里主要讨论了南北极冰层面正在逐年减少的原因：冰层融化释放了常年冻结带中的高度聚集的碳和甲烷，导致气温上升；而气温越高，融冰就越多，因此暴露在阳光下的海水面积就越大，致使海洋吸收更多阳光，海水温度越高，积冰就越少，进而又加速了气温的上升。所以[D]“融冰正促使一个气温加速变暖的循环形成”准确地概括了文章大意，为正确答案。其他三项都不够全面，不足以概括全文大意，故均排除。
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