Most earthquakes occur within the upper 15

问题单项选择题

Most earthquakes occur within the upper 15 miles of the earth’s surface. But earthquakes can and do occur at all depths to about 460 miles. Their number decreases as the depth increases. At about 460 miles one earthquake occurs only every few years. Near the surface earthquakes may run as high as 100 in a month, but the yearly average does not vary much. In comparison with the total number of earthquakes each year, the number of disastrous earthquakes is very small.
The extent of the disaster in an earthquake depends on many factors. If you carefully build a toy house with an erect set, it will still stand no matter how much you shake the table. But if you build a toy house with a pack of cards, a slight shake of the table will make it fall. An earthquake in Agadir, Morocco, was not p enough to be recorded on distant instruments, but it completely destroyed the city. Many per earthquakes have done comparatively little damage. If a building is well constructed and built on solid ground, it will resist an earthquake. Most deaths in earthquakes have been due to faulty building construction or poor building sites. A third and very serious factor is panic. When people rush out into narrow streets, more deaths will result.
The United Nations has played an important part in reducing the damage done by earthquakes. It has sent a team of experts to all countries known to be affected by earthquakes. Working with local geologists and engineers, the experts have studied the nature of the ground and the type of most practical building code for the local area. If followed, these suggestions will make disastrous earthquakes almost a thing of the past.
There is one type of earthquake disaster that little can be done about. This is the disaster caused by seismic sea waves, or tsunamis. (These are often called tidal waves, but the name is incorrect. They have nothing to do with tides.) In certain areas, earthquakes take place beneath the sea. These submarine earthquakes sometimes give rise to seismic sea waves. The waves are not noticeable out at sea because of their long wave length. But when they roll into harbors, they pile up into walls of water 6 to 60 feet high. The Japanese call them "tsunamis", meaning "harbor waves", because they reach a sizable height only in harbors. Tsunamis travel fairly slowly, at speeds up to 500 miles an hour. An adequate warning system is in use to warn all shores likely to be reached by the waves. But this only enables people to leave the threatened shores for higher ground. There is no way to stop the oncoming wave.

The significance of the slow speed of tsunamis is that people may

A．notice them out at sea．

B．find ways to stop them．

C．be warned early enough．

D．develop warning systems．

答案

参考答案：C

解析：本题是一道细节题。文章最后一段讲到了关于海啸的一些情况。该段的第六句指出海啸发生的时候，因为海浪线较长，波浪并不容易察觉(The waves are not noticeable out at sea because of their long wave length)。因此，选项A项是不正确的。在该段的第一句作者就告诉我们海啸是一类让我们束手无策的地震(There is one type of earthquake disaster that little can be done about)。因此B项也是不符合原文的。文章倒数第三句讲到了预警系统：“An adequate warning system is in use to warn all shores likely to be reached by the waves．”因为海啸传递的速度比较慢，所以有足够的时间来警告那些海啸可能会到达的地方。但是如果以前没有设立预警设备的，海啸前进的速度再慢也来不及的。所以可以排除选项D，本题最佳答案是C。