六级冲刺练习：阅读（128）
<p> <span word="This">This</span> <span word="productivity">productivity</span>, <span word="however">however</span>, <span word="has">has</span> <span word="its">its</span> <span word="price">price</span>. <span word="Intensive">Intensive</span> <span word="cultivation">cultivation</span> <span word="exposes">exposes</span> <span word="the">the</span> <span word="earth">earth</span> <span word="to">to</span> <span word="the">the</span> <span word="damaging">damaging</span> <span word="forces">forces</span> <span word="of">of</span> <span word="nature">nature</span>. <span word="Every">Every</span> <span word="year">year</span> <span word="wind">wind</span> <span word="and">and</span> <span word="water">water</span> <span word="remove">remove</span> <span word="tons">tons</span> <span word="of">of</span> <span word="rich">rich</span> <span word="soil">soil</span> <span word="from">from</span> <span word="the">the</span> <span word="nations">nations</span> <span word="croplands">croplands</span>.</p><p> <span word="Each">Each</span> <span word="field">field</span> <span word="is">is</span> <span word="covered">covered</span> <span word="by">by</span> <span word="a">a</span> <span word="limited">limited</span> <span word="amount">amount</span> <span word="of">of</span> <span word="topsoil">topsoil</span>, <span word="the">the</span> <span word="upper">upper</span> <span word="layer">layer</span> <span word="of">of</span> <span word="earth">earth</span> <span word="which">which</span> <span word="is">is</span> <span word="richest">richest</span> <span word="in">in</span> <span word="the">the</span> <span word="nutrients">nutrients</span> <span word="and">and</span> <span word="minerals">minerals</span> <span word="necessary">necessary</span> <span word="for">for</span> <span word="growing">growing</span> <span word="crops">crops</span>. <span word="Ever">Ever</span> <span word="since">since</span> <span word="the">the</span> <span word="first">first</span> <span word="farmers">farmers</span> <span word="arrived">arrived</span> <span word="in">in</span> <span word="the">the</span> <span word="Midwest">Midwest</span> <span word="almost">almost</span> 200 <span word="years">years</span> <span word="ago">ago</span>，<span word="cultivation">cultivation</span> <span word="and">and</span>, <span word="consequently">consequently</span>, <span word="erosion">erosion</span> <span word="have">have</span> <span word="been">been</span> <span word="decreasing">decreasing</span> <span word="the">the</span> <span word="supply">supply</span> <span word="of">of</span> <span word="topsoil">topsoil</span>. <span word="In">In</span> <span word="the">the</span> 1830<span word="s">s</span>, <span word="nearly">nearly</span> <span word="two">two</span> <span word="feet">feet</span> <span word="of">of</span> <span word="rich">rich</span>, <span word="black">black</span> <span word="top">top</span> <span word="soil">soil</span> <span word="covered">covered</span> <span word="the">the</span> <span word="Midwest">Midwest</span>. <span word="Today">Today</span> <span word="the">the</span> <span word="average">average</span> <span word="depth">depth</span> <span word="is">is</span> <span word="only">only</span> <span word="eight">eight</span> <span word="inches">inches</span>, <span word="and">and</span> <span word="every">every</span> <span word="decade">decade</span> <span word="another">another</span> <span word="inch">inch</span> <span word="is">is</span> <span word="blown">blown</span> <span word="or">or</span> <span word="washed">washed</span> <span word="away">away</span>. <span word="This">This</span> <span word="erosion">erosion</span> <span word="is">is</span> <span word="steadily">steadily</span> <span word="decreasing">decreasing</span> <span word="the">the</span> <span word="productivity">productivity</span> <span word="of">of</span> <span word="valuable">valuable</span> <span word="cropland">cropland</span>. <span word="A">A</span> <span word="United">United</span> <span word="States">States</span> <span word="Agricultural">Agricultural</span> <span word="Department">Department</span> <span word="survey">survey</span> <span word="states">states</span> <span word="that">that</span> <span word="if">if</span> <span word="erosion">erosion</span> <span word="continues">continues</span> <span word="at">at</span> <span word="its">its</span> <span word="present">present</span> <span word="rate">rate</span>, <span word="corn">corn</span> <span word="and">and</span> <span word="soybean">soybean</span> <span word="yields">yields</span> <span word="in">in</span> <span word="the">the</span> <span word="Midwest">Midwest</span> <span word="may">may</span> <span word="drop">drop</span> <span word="as">as</span> <span word="much">much</span> <span word="as">as</span> 30 <span word="percent">percent</span> <span word="over">over</span> <span word="the">the</span> <span word="next">next</span> 50 <span word="years">years</span>.</p><p> <span word="So">So</span> <span word="far">far</span>, <span word="farmers">farmers</span> <span word="have">have</span> <span word="been">been</span> <span word="able">able</span> <span word="to">to</span> <span word="compensate">compensate</span> <span word="for">for</span> <span word="the">the</span> <span word="loss">loss</span> <span word="of">of</span> <span word="fertile">fertile</span> <span word="topsoil">topsoil</span> <span word="by">by</span> <span word="applying">applying</span> <span word="more">more</span> <span word="chemical">chemical</span> <span word="fertilizers">fertilizers</span> <span word="to">to</span> <span word="their">their</span> <span word="fields">fields</span>; <span word="however">however</span>, <span word="while">while</span> <span word="this">this</span> <span word="practice">practice</span> <span word="has">has</span> <span word="increased">increased</span> <span word="crop">crop</span> <span word="yields">yields</span>, <span word="it">it</span> <span word="has">has</span> <span word="been">been</span> <span word="devastating">devastating</span> <span word="for">for</span> <span word="ecology">ecology</span>. <span word="Agriculture">Agriculture</span> <span word="has">has</span> <span word="become">become</span> <span word="one">one</span> <span word="of">of</span> <span word="the">the</span> <span word="biggest">biggest</span> <span word="polluters">polluters</span> <span word="of">of</span> <span word="the">the</span> <span word="nations">nations</span> <span word="precious">precious</span> <span word="water">water</span> <span word="supply">supply</span>. <span word="Rivers">Rivers</span>, <span word="lakes">lakes</span>, <span word="and">and</span> <span word="underground">underground</span> <span word="reserves">reserves</span> <span word="of">of</span> <span word="water">water</span> <span word="are">are</span> <span word="being">being</span> <span word="filled">filled</span> <span word="in">in</span> <span word="and">and</span> <span word="poisoned">poisoned</span> <span word="by">by</span> <span word="soil">soil</span> <span word="and">and</span> <span word="chemicals">chemicals</span> <span word="carried">carried</span> <span word="by">by</span> <span word="drainage">drainage</span> <span word="from">from</span> <span word="eroding">eroding</span> <span word="fields">fields</span>. <span word="Furthermore">Furthermore</span>, <span word="fertilizers">fertilizers</span> <span word="only">only</span> <span word="replenish">replenish</span> <span word="the">the</span> <span word="soils">soils</span> <span word="they">they</span> <span word="do">do</span> <span word="not">not</span> <span word="prevent">prevent</span> <span word="its">its</span> <span word="loss">loss</span>.</p>
页:
[1]