【单选题】
GrandCanyon
How was the GrandCanyon formed The truth is that no one knows for sure though there are some pretty good guesses, and it is usually thought that a number of processes combined to create the views that you see in today’s GrandCanyon. The most powerful force to have an impact on the GrandCanyon is erosion, primarily by water (and ice) and secondly by winD、Other forces that contributed to theCanyon’s formation are the course of theColorado River itself, vulcanism, continental drift and slight variations in the earth’s orbit which in turn causes variations in seasons and climate.
Water seems to have had the most impact basically because our planet has lots of it and it is always on the move. Many people cannot understand how water can have such a profound impact considering that theCanyon is basically located in a desert. This is one of the biggest reasons that water has such a big impact here.Because the soil in the GrandCanyon is baked by the sun it tends to become very hard and cannot absorb water when the rains come. When it does rain the water tends to come down in torrents which only add to the problem. The plants that grow in the GrandCanyon tend to have very shallow root systems so that they can grab as much water as possible on those rare occasions when it does rain. Unfortunately these root systems do nothing to deter erosion by holding the soil in place. Now you’ve got lots of water, no place for it to go, but down to theColorado River, and nothing holding the soil and rock in place. The result is frequently a flash flood roaring down a side canyon that can move boulders the size of automobiles, buses and even small houses. If automobiles, buses and small houses are in the way then it will take them too.
A、[■] Luckily no one builds houses in the GrandCanyon so that’s not a problem but there are a few autos, vans and buses sitting at the bottom of theColorado River. This mass that moves down a side canyon during a flash flood is more like fast flowing concrete than water and it can be very dangerous. You should always be well informed of weather conditions when you are hiking through side canyons in the GrandCanyon.
B、[■] In the colder months, especially on the north rim, water seeps into cracks between the rocks. These cracks can be caused by seismic activity, or by the constant soaking and drying of the rocks.
C、[■] When the water freezes it expands and pushes the rocks apart and widens the cracks.Eventually rocks near the rim are pushed off the edge and fall into the side canyons. These rocks sometimes hit other rocks and are stopped but on occasion one fall by a large rock will cause a cascading effect and create a rock fall that will alter the landscape drastically in the side canyon.Debris from rock falls piles up at the bottom of the side canyons and is then carried down to theColorado River the next time there is a flash flooD、Rock falls frequently take out sections of trail in the GrandCanyon requiring the Park Service to close these trails until they can be repaireD、
D、[■]
Once the ice has pushed the rocks off the edge and the water in the flash floods has carried them down to the river, then theColorado itself takes over. The erosive action of theColorado has been severely constrained by the building of the GlenCanyonDam, which ended the annual spring floods, but there is still a lot of water flowing relatively quickly through a very narrow gorge.Before building the dam theColorado River had spring floods that would exceed a flow rate of 100000CFS (cubic feet per second).All of that snow melting in theColorado Rockies came pouring down through the GrandCanyon in May and June every year, like clock-work. These spring floods were considerably larger than today’s "trickle" of 8000～10000CFS at low water and even the 20000CFS peak flow rates. The word
网考网参考答案：B
网考网解析：
[解析] 本题是指代关系题，要求考生认定代词与篇章中其他词语的指代关系。雨量大时爆发的洪水会带走土石，文章还说如果有车辆或房屋的话，也会被卷走的。从原文“The result is frequently a flash flood roaring down a side canyon that can move boulders the size of automobiles...If automobiles...are in the way then it will take them too”可知是被flood卷走，因此选B。选项A、D有一定的干扰性，不过仔细联系上文不难确定it在这里指的是flood。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>
How was the GrandCanyon formed The truth is that no one knows for sure though there are some pretty good guesses, and it is usually thought that a number of processes combined to create the views that you see in today’s GrandCanyon. The most powerful force to have an impact on the GrandCanyon is erosion, primarily by water (and ice) and secondly by winD、Other forces that contributed to theCanyon’s formation are the course of theColorado River itself, vulcanism, continental drift and slight variations in the earth’s orbit which in turn causes variations in seasons and climate.
Water seems to have had the most impact basically because our planet has lots of it and it is always on the move. Many people cannot understand how water can have such a profound impact considering that theCanyon is basically located in a desert. This is one of the biggest reasons that water has such a big impact here.Because the soil in the GrandCanyon is baked by the sun it tends to become very hard and cannot absorb water when the rains come. When it does rain the water tends to come down in torrents which only add to the problem. The plants that grow in the GrandCanyon tend to have very shallow root systems so that they can grab as much water as possible on those rare occasions when it does rain. Unfortunately these root systems do nothing to deter erosion by holding the soil in place. Now you’ve got lots of water, no place for it to go, but down to theColorado River, and nothing holding the soil and rock in place. The result is frequently a flash flood roaring down a side canyon that can move boulders the size of automobiles, buses and even small houses. If automobiles, buses and small houses are in the way then it will take them too.
A、[■] Luckily no one builds houses in the GrandCanyon so that’s not a problem but there are a few autos, vans and buses sitting at the bottom of theColorado River. This mass that moves down a side canyon during a flash flood is more like fast flowing concrete than water and it can be very dangerous. You should always be well informed of weather conditions when you are hiking through side canyons in the GrandCanyon.
B、[■] In the colder months, especially on the north rim, water seeps into cracks between the rocks. These cracks can be caused by seismic activity, or by the constant soaking and drying of the rocks.
C、[■] When the water freezes it expands and pushes the rocks apart and widens the cracks.Eventually rocks near the rim are pushed off the edge and fall into the side canyons. These rocks sometimes hit other rocks and are stopped but on occasion one fall by a large rock will cause a cascading effect and create a rock fall that will alter the landscape drastically in the side canyon.Debris from rock falls piles up at the bottom of the side canyons and is then carried down to theColorado River the next time there is a flash flooD、Rock falls frequently take out sections of trail in the GrandCanyon requiring the Park Service to close these trails until they can be repaireD、
D、[■]
Once the ice has pushed the rocks off the edge and the water in the flash floods has carried them down to the river, then theColorado itself takes over. The erosive action of theColorado has been severely constrained by the building of the GlenCanyonDam, which ended the annual spring floods, but there is still a lot of water flowing relatively quickly through a very narrow gorge.Before building the dam theColorado River had spring floods that would exceed a flow rate of 100000CFS (cubic feet per second).All of that snow melting in theColorado Rockies came pouring down through the GrandCanyon in May and June every year, like clock-work. These spring floods were considerably larger than today’s "trickle" of 8000～10000CFS at low water and even the 20000CFS peak flow rates. The word
网考网参考答案：B
网考网解析：
[解析] 本题是指代关系题，要求考生认定代词与篇章中其他词语的指代关系。雨量大时爆发的洪水会带走土石，文章还说如果有车辆或房屋的话，也会被卷走的。从原文“The result is frequently a flash flood roaring down a side canyon that can move boulders the size of automobiles...If automobiles...are in the way then it will take them too”可知是被flood卷走，因此选B。选项A、D有一定的干扰性，不过仔细联系上文不难确定it在这里指的是flood。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>
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