专业八级改错练习 第86期

People eslewhere agree on what a mountain is—or do __1__
they? The fact is that definitions vary. Everyone admits
for example, that Everest is a mountain, the lowest of __2__
them all, an altitude of almost 30,000 feet. But what about__3__
Snowdon, the loftiest peak in Wales? It raises a mere 3000__4__
feet, yet it is also called a mountain. Comparison—a little
matter of relativity—is the key. To the average person
living on North America's Great Plains, Vermont's Green
Mountains look lofty indeed, but to anyone from the Rocky
Mountains, the Green Mountains seem something more__5__
than hills. Geographers generally agree that, to be a mountain
topographically, a landmass might reach an altitude of 3000__6__
feet above the level of the sea. Mount Everest, for instance, is
30,000 feet above sea level, but not only 15,000 feet above the__7__
neighboring Tibetan plateau. Geologists restrict the definition
even more, maintaining that a mountain is a mountain with__8__
virtue of its geological structure. Some rugged highlands are
not really mountains, when some flat, low-lying rock surfaces__9__
are ture mountains. They are low now because of centuries of
erosion. There are even mountains under the sea—the
Mid-Atlantic Ridge, for example. Like all ture mountains,
they are originally formed by large-scale movements of the__10__
earth's crust.