GRE阅读高频机经原文及试题：蝙蝠的回声定位
<p> 33. 蝙蝠的回声定位</p><p> <span word="Echolocating">Echolocating</span> <span word="bats">bats</span> <span word="emit">emit</span> <span word="sounds">sounds</span> <span word="in">in</span> <span word="patternscharacteristic">patternscharacteristic</span> <span word="of">of</span> <span word="each">each</span> <span word="speciesthat">speciesthat</span> <span word="contain">contain</span> <span word="both">both</span> <span word="frequency">frequency</span>-<span word="modulated">modulated</span> <span word="and">and</span> <span word="constant">constant</span>-<span word="frequency">frequency</span> <span word="signals">signals</span>. <span word="The">The</span> <span word="broadband">broadband</span> <span word="FM">FM</span> <span word="signals">signals</span> <span word="and">and</span> <span word="the">the</span> <span word="narrowband">narrowband</span> <span word="CF">CF</span> <span word="signals">signals</span> <span word="travel">travel</span> <span word="out">out</span> <span word="to">to</span> <span word="a">a</span> <span word="target">target</span>, <span word="reflect">reflect</span> <span word="from">from</span> <span word="it">it</span>, <span word="and">and</span> <span word="return">return</span> <span word="to">to</span> <span word="the">the</span> <span word="hunting">hunting</span> <span word="bat">bat</span>. <span word="In">In</span> <span word="this">this</span> <span word="process">process</span> <span word="of">of</span> <span word="transmission">transmission</span> <span word="and">and</span> <span word="reflection">reflection</span>, <span word="the">the</span> <span word="sounds">sounds</span> <span word="are">are</span> <span word="changed">changed</span>, <span word="and">and</span> <span word="the">the</span> <span word="changes">changes</span> <span word="in">in</span> <span word="the">the</span> <span word="echoes">echoes</span> <span word="enable">enable</span> <span word="the">the</span> <span word="bat">bat</span> <span word="to">to</span> <span word="perceive">perceive</span> <span word="features">features</span> <span word="of">of</span> <span word="the">the</span> <span word="target">target</span>.</p><p> <span word="The">The</span> <span word="FM">FM</span> <span word="signals">signals</span> <span word="report">report</span> <span word="information">information</span> <span word="about">about</span> <span word="target">target</span> <span word="characteristics">characteristics</span> <span word="that">that</span> <span word="modify">modify</span> <span word="the">the</span> <span word="timing">timing</span> <span word="and">and</span> <span word="the">the</span> <span word="fine">fine</span> <span word="frequency">frequency</span> <span word="structure">structure</span>, <span word="or">or</span> <span word="spectrum">spectrum</span>, <span word="of">of</span> <span word="echoesfor">echoesfor</span> <span word="example">example</span>, <span word="the">the</span> <span word="targets">targets</span> <span word="size">size</span>, <span word="shape">shape</span>, <span word="texture">texture</span>, <span word="surface">surface</span> <span word="structure">structure</span>, <span word="and">and</span> <span word="direction">direction</span> <span word="in">in</span> <span word="space">space</span>. <span word="Because">Because</span> <span word="of">of</span> <span word="their">their</span> <span word="narrow">narrow</span> <span word="bandwidth">bandwidth</span>, <span word="CF">CF</span> <span word="signals">signals</span> <span word="portray">portray</span> <span word="only">only</span> <span word="the">the</span> <span word="targets">targets</span> <span word="presence">presence</span> <span word="and">and</span>, <span word="in">in</span> <span word="the">the</span> <span word="case">case</span> <span word="of">of</span> <span word="some">some</span> <span word="bat">bat</span> <span word="species">species</span>, <span word="its">its</span> <span word="motion">motion</span> <span word="relative">relative</span> <span word="to">to</span> <span word="the">the</span> <span word="bats">bats</span>. <span word="Responding">Responding</span> <span word="to">to</span> <span word="changes">changes</span> <span word="in">in</span> <span word="the">the</span> <span word="CF">CF</span> <span word="echos">echos</span> <span word="frequency">frequency</span>, <span word="bats">bats</span> <span word="of">of</span> <span word="some">some</span> <span word="species">species</span> <span word="correct">correct</span> <span word="in">in</span> <span word="flight">flight</span> <span word="for">for</span> <span word="the">the</span> <span word="direction">direction</span> <span word="and">and</span> <span word="velocity">velocity</span> <span word="of">of</span> <span word="their">their</span> <span word="moving">moving</span> <span word="prey">prey</span>.</p><p> 33.1. <span word="According">According</span> <span word="to">to</span> <span word="the">the</span> <span word="passage">passage</span>, <span word="the">the</span> <span word="information">information</span> <span word="provided">provided</span> <span word="to">to</span> <span word="the">the</span> <span word="bat">bat</span> <span word="by">by</span> <span word="CF">CF</span> <span word="echoes">echoes</span> <span word="differs">differs</span> <span word="from">from</span> <span word="that">that</span> <span word="provided">provided</span> <span word="by">by</span> <span word="FM">FM</span> <span word="echoes">echoes</span> <span word="in">in</span> <span word="which">which</span> <span word="of">of</span> <span word="the">the</span> <span word="following">following</span> <span word="ways">ways</span>?</p><p> <span word="Only">Only</span> <span word="CF">CF</span> <span word="echoes">echoes</span> <span word="alert">alert</span> <span word="the">the</span> <span word="bat">bat</span> <span word="to">to</span> <span word="moving">moving</span> <span word="targets">targets</span>.</p><p> <span word="Only">Only</span> <span word="CF">CF</span> <span word="echoes">echoes</span> <span word="identify">identify</span> <span word="the">the</span> <span word="range">range</span> <span word="of">of</span> <span word="widely">widely</span> <span word="spaced">spaced</span> <span word="targets">targets</span>.</p><p> <span word="Only">Only</span> <span word="CF">CF</span> <span word="echoes">echoes</span> <span word="report">report</span> <span word="the">the</span> <span word="targets">targets</span> <span word="presence">presence</span> <span word="to">to</span> <span word="the">the</span> <span word="bat">bat</span>.</p><p> <span word="In">In</span> <span word="some">some</span> <span word="species">species</span>, <span word="CF">CF</span> <span word="echoes">echoes</span> <span word="enable">enable</span> <span word="the">the</span> <span word="bat">bat</span> <span word="to">to</span> <span word="judge">judge</span> <span word="whether">whether</span> <span word="it">it</span> <span word="is">is</span> <span word="closing">closing</span> <span word="in">in</span> <span word="on">on</span> <span word="its">its</span> <span word="target">target</span>.</p>
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