六级冲刺练习：阅读（137）
<p> <span word="Erosion">Erosion</span> <span word="levels">levels</span> <span word="the">the</span> <span word="earths">earths</span> <span word="surface">surface</span>. <span word="Essentially">Essentially</span>, <span word="erosion">erosion</span> <span word="is">is</span> <span word="the">the</span> <span word="natural">natural</span> <span word="process">process</span> <span word="that">that</span> <span word="ceaselessly">ceaselessly</span> <span word="tries">tries</span> <span word="to">to</span> <span word="level">level</span> <span word="the">the</span> <span word="earths">earths</span> <span word="surface">surface</span>. <span word="If">If</span> <span word="it">it</span> <span word="were">were</span> <span word="not">not</span> <span word="for">for</span> <span word="other">other</span> <span word="forces">forces</span> <span word="also">also</span> <span word="constantly">constantly</span> <span word="at">at</span> <span word="work">work</span>, <span word="the">the</span> <span word="mountains">mountains</span> <span word="and">and</span> <span word="hills">hills</span> <span word="would">would</span> <span word="eventually">eventually</span> <span word="disappear">disappear</span> <span word="and">and</span> <span word="all">all</span> <span word="of">of</span> <span word="the">the</span> <span word="land">land</span> <span word="would">would</span> <span word="be">be</span> <span word="under">under</span> <span word="water">water</span>. <span word="Fortunately">Fortunately</span>, <span word="however">however</span>, <span word="many">many</span> <span word="areas">areas</span> <span word="of">of</span> <span word="the">the</span> <span word="earths">earths</span> <span word="surface">surface</span> <span word="are">are</span> <span word="being">being</span> <span word="raised">raised</span> <span word="by">by</span> <span word="volcanic">volcanic</span> <span word="action">action</span> <span word="and">and</span> <span word="by">by</span> <span word="balancing">balancing</span> <span word="movements">movements</span> <span word="of">of</span> <span word="the">the</span> <span word="earths">earths</span> <span word="crust">crust</span>. <span word="For">For</span> <span word="example">example</span>, <span word="great">great</span> <span word="pressures">pressures</span> <span word="exerted">exerted</span> <span word="by">by</span> <span word="the">the</span> <span word="water">water</span> <span word="and">and</span> <span word="sediments">sediments</span> <span word="on">on</span> <span word="the">the</span> <span word="ocean">ocean</span> <span word="floor">floor</span> <span word="along">along</span> <span word="many">many</span> <span word="shorelines">shorelines</span> <span word="result">result</span> <span word="in">in</span> <span word="forces">forces</span> <span word="that">that</span> <span word="cause">cause</span> <span word="the">the</span> <span word="land">land</span> <span word="area">area</span> <span word="to">to</span> <span word="be">be</span> <span word="uplifted">uplifted</span>. <span word="Thus">Thus</span> <span word="erosion">erosion</span> <span word="never">never</span> <span word="completely">completely</span> <span word="succeeds">succeeds</span> <span word="in">in</span> <span word="leveling">leveling</span> <span word="the">the</span> <span word="earths">earths</span> <span word="surface">surface</span>.</p><p> <span word="Gravity">Gravity</span> <span word="is">is</span> <span word="influential">influential</span>. <span word="The">The</span> <span word="force">force</span> <span word="of">of</span> <span word="gravity">gravity</span> <span word="is">is</span> <span word="responsible">responsible</span> <span word="for">for</span> <span word="both">both</span> <span word="the">the</span> <span word="falling">falling</span> <span word="of">of</span> <span word="rain">rain</span> <span word="from">from</span> <span word="the">the</span> <span word="clouds">clouds</span> <span word="and">and</span> <span word="for">for</span> <span word="the">the</span> <span word="water">water</span> <span word="running">running</span> <span word="off">off</span> <span word="the">the</span> <span word="land">land</span> <span word="as">as</span> <span word="it">it</span> <span word="always">always</span> <span word="seeks">seeks</span> <span word="a">a</span> <span word="lower">lower</span> <span word="level">level</span>. <span word="Likewise">Likewise</span>, <span word="the">the</span> <span word="great">great</span> <span word="moving">moving</span> <span word="currents">currents</span> <span word="of">of</span> <span word="air">air</span> <span word="that">that</span> <span word="we">we</span> <span word="call">call</span> <span word="winds">winds</span> <span word="are">are</span> <span word="the">the</span> <span word="result">result</span> <span word="of">of</span> <span word="unequal">unequal</span> <span word="heating">heating</span> <span word="of">of</span> <span word="the">the</span> <span word="earths">earths</span> <span word="surface">surface</span> <span word="and">and</span> <span word="the">the</span> <span word="convection">convection</span> <span word="currents">currents</span> <span word="that">that</span> <span word="are">are</span> <span word="set">set</span> <span word="up">up</span> <span word="in">in</span> <span word="the">the</span> <span word="atmosphere">atmosphere</span>. <span word="Here">Here</span> <span word="again">again</span> <span word="the">the</span> <span word="force">force</span> <span word="of">of</span> <span word="gravity">gravity</span> <span word="is">is</span> <span word="responsible">responsible</span> <span word="for">for</span> <span word="the">the</span> <span word="downward">downward</span> <span word="movement">movement</span> <span word="of">of</span> <span word="the">the</span> <span word="cooler">cooler</span>, <span word="denser">denser</span> <span word="air">air</span> <span word="toward">toward</span> <span word="the">the</span> <span word="earth">earth</span> <span word="which">which</span> <span word="starts">starts</span> <span word="the">the</span> <span word="air">air</span> <span word="moving">moving</span>.</p><p> <span word="As">As</span> <span word="long">long</span> <span word="as">as</span> <span word="the">the</span> <span word="winds">winds</span> <span word="blow">blow</span> <span word="and">and</span> <span word="rain">rain</span> <span word="falls">falls</span>, <span word="erosion">erosion</span> <span word="will">will</span> <span word="continue">continue</span> <span word="to">to</span> <span word="take">take</span> <span word="place">place</span>. <span word="How">How</span> <span word="is">is</span> <span word="erosion">erosion</span> <span word="useful">useful</span> <span word="to">to</span> <span word="man">man</span> <span word="and">and</span> <span word="when">when</span> <span word="does">does</span> <span word="it">it</span> <span word="become">become</span> <span word="a">a</span> <span word="serious">serious</span> <span word="problem">problem</span>?</p><p> <span word="Erosion">Erosion</span> <span word="works">works</span> <span word="with">with</span> <span word="weathering">weathering</span>. <span word="Erosion">Erosion</span> <span word="works">works</span> <span word="hand">hand</span> <span word="in">in</span> <span word="hand">hand</span> <span word="with">with</span> <span word="the">the</span> <span word="process">process</span> <span word="of">of</span> <span word="weathering">weathering</span> <span word="in">in</span> <span word="causing">causing</span> <span word="rocks">rocks</span> <span word="to">to</span> <span word="be">be</span> <span word="broken">broken</span> <span word="up">up</span> <span word="and">and</span> <span word="changed">changed</span> <span word="into">into</span> <span word="soil">soil</span>. <span word="It">It</span> <span word="is">is</span> <span word="the">the</span> <span word="agents">agents</span> <span word="of">of</span> <span word="erosion">erosion</span> <span word="that">that</span> <span word="carry">carry</span> <span word="away">away</span> <span word="this">this</span> <span word="newly">newly</span> <span word="formed">formed</span> <span word="soil">soil</span> <span word="and">and</span> <span word="expose">expose</span> <span word="fresh">fresh</span> <span word="rock">rock</span> <span word="surfaces">surfaces</span> <span word="to">to</span> <span word="the">the</span> <span word="agents">agents</span> <span word="of">of</span> <span word="weathering">weathering</span>. <span word="Thus">Thus</span> <span word="new">new</span> <span word="rock">rock</span> <span word="surfaces">surfaces</span> <span word="are">are</span> <span word="exposed">exposed</span> <span word="to">to</span> <span word="the">the</span> <span word="air">air</span>, <span word="to">to</span> <span word="rapid">rapid</span> <span word="changes">changes</span> <span word="in">in</span> <span word="temperature">temperature</span>, <span word="to">to</span> <span word="the">the</span> <span word="pounding">pounding</span> <span word="rain">rain</span> <span word="and">and</span> <span word="driving">driving</span> <span word="wind">wind</span>, <span word="to">to</span> <span word="dissolved">dissolved</span> <span word="chemicals">chemicals</span> <span word="in">in</span> <span word="ground">ground</span> <span word="water">water</span>, <span word="and">and</span> <span word="to">to</span> <span word="the">the</span> <span word="other">other</span> <span word="agents">agents</span> <span word="that">that</span> <span word="help">help</span> <span word="in">in</span> <span word="making">making</span> <span word="more">more</span> <span word="soil">soil</span>. <span word="This">This</span> <span word="transported">transported</span> <span word="soil">soil</span> <span word="often">often</span> <span word="ends">ends</span> <span word="up">up</span> <span word="in">in</span> <span word="the">the</span> <span word="fertile">fertile</span> <span word="river">river</span> <span word="valleys">valleys</span> <span word="and">and</span> <span word="plains">plains</span> <span word="where">where</span> <span word="we">we</span> <span word="find">find</span> <span word="our">our</span> <span word="most">most</span> <span word="productive">productive</span> <span word="farmlands">farmlands</span>. <span word="In">In</span> <span word="this">this</span> <span word="process">process</span> <span word="of">of</span> <span word="transporting">transporting</span> <span word="new">new</span> <span word="soil">soil</span> <span word="and">and</span> <span word="minerals">minerals</span> <span word="from">from</span> <span word="where">where</span> <span word="they">they</span> <span word="have">have</span> <span word="been">been</span> <span word="made">made</span> <span word="to">to</span> <span word="where">where</span> <span word="they">they</span> <span word="can">can</span> <span word="be">be</span> <span word="used">used</span>, <span word="erosion">erosion</span> <span word="is">is</span> <span word="useful">useful</span> <span word="to">to</span> <span word="man">man</span>.</p>
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