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  3. Scientists have begun using satellite-based systems to predict volcanic eruptions. This allows blanket coverage of the entire wo

Scientists have begun using satellite-based systems to predict volcanic eruptions. This allows blanket coverage of the entire wo

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问题     Scientists have begun using satellite-based systems to predict volcanic eruptions. This allows blanket coverage of the entire world. Envisat is the most advanced craft of this type. It has sensors that, by recognizing the characteristic optical signature of various substances in the atmosphere, can detect the presence of specific gases, such as sulphur dioxide. These may indicate an imminent volcanic eruption.
    Mike Abrams, a scientist at America’s space agency, NASA, says that the limiting factor on all such satellites is, surprisingly, not technological, but temporal. The orbits in which they are placed allow them to observe the entire earth, but they cannot pass over a particular spot more frequently than once every 15 days or so. Dr. Abrams argues that more satellites are needed to gather sufficient data on the earth’s volcanoes. Existing satellites, though, do at least serve as an early warning system. If one of them detects something amiss, local volcanologists can then intensify their local monitoring efforts. If necessary, they can even initiate an evacuation.
    In addition, it is important to predict lahars, flowing mixtures of rock, debris, ash and water, which are often set off when hot lava meets cold snow. Lahars can travel down a mountain as fast as 60 kilometres per hour. In 1985 a lahar set off by the eruption of the Nevada del Ruiz volcano in Colombia killed 25,000 people. With acoustic flow monitors, such as those developed by the USGS in the last five years, such a tragic loss of life might have been averted. The flow monitors are seismometers, which measure vibration, and are sensitive to higher frequencies than those used to record earthquakes and volcanic activity. This lets them hear lahars from a long way off, creating a valuable extra hour of time that can be used to evacuate. Such systems are now in place all round the world.
    Volcanic eruptions are dangerous not only to people on the ground, but also to those in the air. According to the USGS, more than 80 commercial aircraft have run into unexpected volcanic ash in the past 15 years, with the resulting damage costing hundreds of millions of dollars. If the optimists are right, the threat from volcanoes could one day become a known one. There is a problem, though. The work that needs to be done relies on the continual use of satellites and ground monitoring. Volcanologists are now issuing a new warning: that it is particularly hard to get funding for this kind of work. This is something that everybody should be bothered about.
What is this passage mainly about?
选项 A、Effective control over volcanic eruptions.
B、Effective prediction about lahars.
C、Damage of volcanic eruptions to human beings.
D、Perspective of prediction about volcanic eruptions.
答案D
解析 本文的主要内容是什么?[A]对火山爆发的有效控制。[B]对火山泥流的有效预测。[C]火山爆发对人类造成的损害。[D]预测火山爆发的角度。这篇文章主要讲述了科学家们利用卫星系统预测火山爆发。文章还讲述了利用卫星预测的制约因素，不过，目前的卫星至少可以用作预警系统。另外，文章还讲了利用流动监控系统对火山泥流的预测。但作者在文章最后讲了火山预测的前景令人担忧，资金问题得不到落实，这也是本文的主旨所在。因此，正确答案为[D]。[A]不完全正确，因为文章并没有提出对火山爆发的有效控制办法，只是利用卫星系统和地面监控系统就火山爆发提出警告；[B]不完全正确，因为对火山泥流的有效预测只是文章的一部分，而不是全部；[C]也不正确，文章主要通过讲述火山爆发的危害性说明预测火山爆发的必要性。
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