托福阅读真题+题目+答案：Ceology's Impact on the Economy of the United States

托福阅读真题+题目+答案：Ceology's Impact on the Economy of the United States

Geology's Impact on the Economy of the United States The United States has benefited economically from a number of developments in its geological history.Consider first the birth of the Rocky Mountains and its effect on the biogeography of the Great Plains,which reach from the eastern edge of the Rocky Mountains in the West to the Mississippi River in the East,and which have contributed enormously to agricultural productivity.Before the creation of the mountains,a process geologists refer to as the Laramide orogeny,beginning some 80 million years ago,the region now known as the Great Plains was a tremendous inland sea.The emergence of the Rockies,however,plugged the water's entry from the Pacific and Arctic oceans,creating conditions favorable to the eventual emergence of forest cover on the plains.The mountains also dried out the land by capturing the moisture of the clouds on their western side,creating a huge rain shadow that left the plains to the east in an even more arid state,precisely an environment suitable for the growth of grass.Meanwhile,the rain that did fall in the mountains washed away sediments and deposited them further east with each passing year,covering the old seabed with a layer of loose silt that was hundreds of feet thick and producing in the process one of the most level stretches of land on Earth.The Rockies,by drying out the landscape of the plains,encouraged the growth of grasses,which, due to complicated root systems that can exploit even the smallest amount of moisture,flourish in such an environment.Into these grasslands the American pioneer eventually forged,prepared to break the sod and replace it with another grass:the wheat so fabulously adapted to life in an arid locale.

1.All of the following are mentioned in paragraph 1 as effects of the Laramide orogeny process EXCEPT

O a reduction in rainfall east of the Rocky Mountains

O the cutoff of the water supply that fed the inland sea

O the widening of the Mississippi River

O the formation of a layer of silt on the Great Plains

2.According to paragraph 1,why does wheat grow well in the Great Plains?

O It tolerates considerable variation in moisture levels.

O It requires relatively little water to survive.

O It has a minimal root system in comparison with other grasses.

O It can grow in almost any kind of soil.

That was not all the Laramide mountain-building episode did to contribute to America's economic strength.It also broke up granite and metamorphic rocks,allowing metallic minerals to insinuate themselves into the faults left behind.Deposits of gold,silver,zinc, lead,and copper settled that much nearer Earth's surface,where they could be mined with relative ease.Without this geological episode, there would have been no Colorado gold rush in the 1850s,no mineral belt running through that state.The Laramide revolution was but one geological event on the nation's road to wealth.Taken together,the combined effect of the region's geological history accounts for North America's near total self-sufficiency in minerals.

3.Paragraph 2 supports which of the following statements about the Laramide orogeny process?

O It removed a belt of minerals in what is now Colorado.

O It slowed the breakup of rocks.

O It threatened America's economic growth.

O It allowed metals to collect in easily mined deposits near the surface.

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