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  3. 【C1】______. This challenge remains and contemporary seismologists continue to seek reliable methods for pinpointing the time, pl

【C1】______. This challenge remains and contemporary seismologists continue to seek reliable methods for pinpointing the time, pl

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问题     【C1】______. This challenge remains and contemporary seismologists continue to seek reliable methods for pinpointing the time, place and magnitude of individual quakes.
    【C2】______. Earthquakes are concentrated in certain areas of the world where tectonic plates such as the Pacific Plate, the Eurasian Plate and the African Plate meet and create fault zones and it is in these areas that seismologists focus their investigations.
    The plate tectonics model provides another tool for earthquake prediction by calculating the accumulated strain at plate boundaries.【C3】______.
    The search for premonitory phenomena has received particular attention. In contrast to the ancient Greeks and Romans, who relied on the howling of dogs as a warning sign, modern seismologists have focused on physical evidence for an impending earthquake. Evidence of plate strain can be found by measuring relative movements in geodetic stations, while chemical changes also offer signals for seismologists. Using chemical detection techniques, Professor Ulomov established a link between the rise in the concentration of radon gas in mineral water in the Tashken Basin and the subsequent earthquake in 1996.
    Analysis of the changes in magnetic properties and conductivity of rocks provides further data for prediction. The electrical and magnetic properties of crustal rocks are particularly sensitive to strain and studies measuring changes which occur in these properties have provided promising results. The conductivity of crustal rock is determined by the degree to which the rock is saturated with fluid and the electrolytic properties of those fluids. Before large earthquakes, small fractures develop in rocks which changes the quantity of fluid present. These changes can be measured and provide useful predictive data. However, similar changes in the fluid-bearing capacity of rock can occur as a result of other factors such as changes in the water table, and therefore this technique is not entirely reliable.
    The ancient belief that the behavior of birds, cats and dogs provides evidence of imminent earthquakes has recently gained credence as a result of tests carried out in California. It has been shown that changes take place in the metabolic rates of these animals which correlate with subsequent seismic activity.【C4】______
    In zones where earthquakes are known to occur, improved construction techniques can significantly reduce the effects of seismic waves. If more accurate information regarding the time and magnitude were available, governments could take even more effective measures to reduce the impact on human life.【C5】______
[A] Since antiquity, the devastating effects of earthquakes on human lives and property have encouraged the search for reliable methods of earthquake prediction.
[B] Another tool for earthquake prediction is the behavior of not only birds, cats and dogs, but also some persons.
[C] When the strain reaches a certain magnitude the pressure must be released and it is therefore hypothesized that in such cases an earthquake is imminent.
[D] One prediction technique involves analysis of the recurrence rates of earthquakes as indicators of future seismic activity.
[E] If, however, an entirely accurate prediction technique became available, there would be significant social and political implications. An earthquake prediction in a major urban area, for example, would require governments to provide an effective evacuation strategy, necessitating massive resourcing and political will.
[F] It is hypothesized that the animals are sensitive to the seismic waves which precede major quakes.
【C2】
选项
答案D
解析 本空白处应为第二段的主题句。下文说到科学家们重点研究几大板块交界地带的地震活动，浏览各项，[D]中的“对地震复发率的分析是预测地震的方法之一”恰好是对本段的概括，故为答案。
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