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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.
By saying "more satellites are needed to gather sufficient data on the earth’s volcanoes", Dr. Abrams implies that
选项 A、more satellites have already been used to observe the entire earth.
B、the frequency of satellites’ passing over a particular spot is too low.
C、to predict volcanic eruptions is difficult.
D、satellites used to predict volcanic eruptions are not sufficient.
答案D
解析 艾伯拉穆斯博士说more satellites are needed to gather sufficient data on theearth’s volcanoes这句话暗含的意思是：[A]更多的卫星已被用来观察整个地球。[B]卫星通过特定位置的频率太低。[C]预测火山爆发非常困难。[D]被用来预测火山爆发的卫星还不够。文章第二段指出，艾伯拉穆斯博士说，这些卫星的制约因素不在于技术，而在于时间。他认为，需要更多的卫星收集地球上足够的火山资料。他的话暗示了用来预测火山爆发的卫星还不是很多，因此他希望有更多的卫星用来收集资料，以弥补利用卫星预测的时间上的制约。因此，正确答案是[D]。我们无法从艾伯拉穆斯的话中推断出[A]．[B]“卫星通过特定位置的频率太低”是利用卫星预测的制约因素，但艾伯拉穆斯的话并没有表明这个制约因素；[C]是事实，可是艾伯拉穆斯的话是要求有更多的卫星来收集资料。
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