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【单选题】
Eight times within the past million years, something in the Earth's climatic equation has changed, allowing snow in the mountains and the northern latitudes to accumulate from one season to the next instead of melting away. Each time, the enormous ice sheets resulting from this continual buildup lasted tens of thousands of years until the end of each particular glacial cycle brought a warmer climate. Scientists speculated that these glacial cycles were ultimately driven by astronomical factor: slow, cyclic changes in the eccentricity of the Earth's orbit and in the tilt and orientation of its spin axis. But up until around 30 years ago, the lack of an independent record of ice-age timing made the hypothesis untestable. Then in the early 1950's Emiliani produced the first complete record of the waxings and wanings of first glaciations. It came from a seemingly odd place, the seafloor. Single-cell marine organisms called 'foraminifera' house themselves in shells made from calcium carbonate. When the foraminifera die, sink to the bottom, and become part of seafloor sediments, the carbonate of their shells preserves certain characteristics of the seawater they inhabited. In particular, the ratio of a heavy isotope of oxygen (oxygen-18) to ordinary oxygen (oxygen-16) in the carbonate preserves the ratio of the two oxygens in water molecules. It is now understood that the ratio of oxygen isotopes reflects the proportion of the world's water locked up in glaciers and ice sheets. A kind of meteorological distillation accounts for the link. Water molecules containing the heavier isotope tend to condense and fall as precipitation slightly sooner than molecules containing the lighter isotope. Hence, as water vapor evaporated from warm oceans moves away from its source, its oxygen- 18 returns more quickly to the oceans than does its oxygen-16. What falls as snow on distant ice sheets and mountain glaciers is relatively depleted of oxygen-18. As the oxygen-18-poor ice builds up, the oceans become relatively enriched in the isotope. The larger the ice sheets grow, the higher the proportion of oxygen-18 becomes in seawater--and hence in the sediments Analyzing cores drilled from seafloor sediments, Emiliani found that the isotopic ratio rose and fell in rough accord with the Earth's astronomical cycles. Since that pioneering observation, oxygenisotope measurements have been made on hundreds of cores. The combined record enables scientists to show that the re-cord contains the very periodicities as the orbital processes. Over the past 800, 000 years, the global ice volume peaked every 100,000 years, matching the period of the orbital eccentricity variation. In addition, 'wrinkles' superposed on each cycle--small decreases or surges in ice volume--have come at intervals of roughly 23,000 and 41,000 years, in keeping with the precession and tilt frequencies of the Earth's spin axis. In opening paragraph, the author introduces his topic by ______
A.
unfolding a phenomenon.
B.
posing a contrast.
C.
refuting a speculation.
D.
testifying a hypothesis.
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【多选题】休闲型派对的着装应选择( )。
A.
牛仔装
B.
时装
C.
休闲装
D.
礼服
【单选题】理想的压缩蒸汽冷冻机的工作过程为
A.
绝热压缩→等温放热→绝热膨胀→等温吸热
B.
等温放热→等温吸热→绝热压缩→绝热膨胀
C.
等温吸热 → 绝热膨胀 → 等温放热 → 绝热压缩
【单选题】理想的压缩蒸汽冷冻机的工作过程为( )。
A.
绝热压缩一等温放热一绝热膨胀一等温吸热
B.
等温放热一等温吸热一绝热压缩一绝热膨胀
C.
等温吸热一绝热膨胀一等温放热一绝热压缩
D.
等温吸热一绝热压缩一等温放热一绝热膨胀
【单选题】休闲型派对的着装应选择下列哪一种款式()
A.
牛仔装
B.
时装
C.
礼服
D.
正装
【多选题】阅读材料,回答问题:该论述不符合()。【“我觉得,中国人不要过分去追求诺贝尔奖。我所从事的物理学分支每隔三四年就有一次诺贝尔奖,但是这些研究拿到中国来,国家不可能支持。这是对的。因为当前中国更需要解决的是国计民生问题。基础研究要花很多钱,这些钱投下去很难解决当前最迫切的问题。我们是发展中国家,可以从发达国家搞的一些基础研究中挑选出来有用的东西,拿过来。基础研究在科学上有意义,有的在10年20年以后...
A.
论题的表达必须清楚、准确,在论证中保持前后一致。
B.
论题的知识范围要比论据的知识范围小。
C.
论证所运用的推理中,所有前提必须是真实的或者是交流的双方可接受的。
D.
论证中论据必须彼此一致和相容,不能出现前后不一致或相反的断言。
【单选题】理想的压缩蒸汽冷冻机的工作过程为( )。
A.
绝热压缩→等温放热→绝热膨胀→等温吸热
B.
等温放热→等温吸热→绝热压缩→绝热膨胀
C.
等温吸热→绝热膨胀→等温放热→绝热压缩
D.
绝热压缩→绝热膨胀→等温放热→等温吸热
【简答题】You actually trust it to __________ ______ _____ ______ again.
【简答题】自己独立制作求职自荐书封面
【多选题】休闲型派对的着装应选择
A.
牛仔装
B.
时装
C.
运动装
D.
礼服
E.
休闲装
【单选题】理想的压缩蒸汽冷冻机的工作过程为( )。
A.
绝热压缩一等温放热一绝热膨胀一等温吸热
B.
等温放热一等温吸热一绝热压缩一绝热膨胀
C.
等温吸热一绝热膨胀一等温放热一绝热压缩
D.
绝热压缩一绝热膨胀一等温放热一等温吸热
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