Many geologists theorize that the trail of volcanic craters and cinder cones along theSnake River plain of sourthern Idaho was produced as the North American continent slid westward over a ststionary"plume," a veritical channel through which molten rock rose intermittently from the Earth's core to brust through its crust.
Which of the following, if true, tends to support the geologists' theory of how the trail was produced?
a) The largest craters and cinder cones are on the eastern margin if the trail.
b) The most violent volcanic activity apparently occurred at the western margin of the trail.
c) The craters and cinder cones are evenly apaced throughout the extent of the trail.
d) The newesr craters and cinder cones are on the western margin of the trail.
e)The craters and cinder cones on the western margin of the trail generally took longer to form than did those on the eastern margin.
The answer is correct. (d) suggest that the newest craters are on the western margin just because the American continent is sliding toward western so that the crashed crust broke and emit the craters.
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发表于 2003-9-30 00:51:00
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