2015考研英语阅读45岁也能生娃
<p> <span word="Life">Life</span> <span word="begins">begins</span> <span word="at">at</span> 45</p><p> 45岁也能生娃</p><p> <span word="Hope">Hope</span> <span word="for">for</span> <span word="older">older</span> <span word="mothers">mothers</span>.</p><p> 高龄母亲的福音。</p><p> <span word="WHEN">WHEN</span> <span word="it">it</span> <span word="comes">comes</span> <span word="to">to</span> <span word="reproduction">reproduction</span>, <span word="men">men</span> <span word="have">have</span> <span word="iteasy">iteasy</span>. <span word="Almost">Almost</span> <span word="to">to</span> <span word="the">the</span> <span word="end">end</span> <span word="of">of</span> <span word="their">their</span> <span word="lives">lives</span> <span word="most">most</span> <span word="have">have</span> <span word="anample">anample</span> <span word="supply">supply</span> <span word="of">of</span> <span word="sperm">sperm</span>. <span word="Women">Women</span> <span word="are">are</span> <span word="not">not</span> <span word="so">so</span> <span word="lucky">lucky</span>.<span word="They">They</span> <span word="are">are</span> <span word="born">born</span> <span word="with">with</span> <span word="a">a</span> <span word="supply">supply</span> <span word="of">of</span> <span word="eggs">eggs</span> <span word="that">that</span> <span word="typically">typically</span> <span word="runs">runs</span> <span word="out">out</span> <span word="when">when</span> <span word="they">they</span> <span word="reach">reach</span> <span word="middle">middle</span> <span word="age">age</span>. <span word="Thatcould">Thatcould</span> <span word="be">be</span> <span word="about">about</span> <span word="to">to</span> <span word="change">change</span>, <span word="however">however</span>. <span word="Researchers">Researchers</span> <span word="have">have</span> <span word="confirmed">confirmed</span> <span word="that">that</span> <span word="women">women</span> <span word="harbourovarian">harbourovarian</span> <span word="stem">stem</span> <span word="cells">cells</span>, <span word="and">and</span> <span word="that">that</span> <span word="these">these</span> <span word="can">can</span> <span word="give">give</span> <span word="rise">rise</span> <span word="to">to</span> <span word="new">new</span> <span word="eggs">eggs</span>.</p><p> 讲到繁衍，男人表示压力很小。大多数人直到去世前都拥有充足的精子。女人可就没这么幸运了。人到中年，她们就会耗尽出生时携带的卵子。不过，这一情形很快就能得到改变。研究者们证实，女人拥有卵巢干细胞，而这种细胞能成为新的卵细胞的来源。</p><p> <span word="Stem">Stem</span> <span word="cells">cells</span> <span word="have">have</span> <span word="the">the</span> <span word="ability">ability</span> <span word="to">to</span> <span word="divide">divide</span> <span word="continuously">continuously</span> <span word="and">and</span> <span word="to">to</span> <span word="change">change</span> <span word="into">into</span> <span word="different">different</span> <span word="types">types</span> <span word="of">of</span> <span word="cells">cells</span>.<span word="Stem">Stem</span> <span word="cells">cells</span> <span word="from">from</span> <span word="adults">adults</span> <span word="can">can</span> <span word="produce">produce</span> <span word="a">a</span> <span word="variety">variety</span> <span word="of">of</span> <span word="cell">cell</span> <span word="types">types</span>, <span word="in">in</span> <span word="addition">addition</span> <span word="to">to</span> <span word="those">those</span> <span word="that">that</span> <span word="makeup">makeup</span> <span word="the">the</span> <span word="tissue">tissue</span> <span word="in">in</span> <span word="which">which</span> <span word="they">they</span> <span word="are">are</span> <span word="found">found</span>.</p><p> 干细胞具有不断分裂的潜力，可以分化成许多种类的细胞。成人干细胞不仅可以分化成其来源组织的细胞，还能分化成其它细胞。</p><p> <span word="In">In</span> 2004 <span word="Jonathan">Jonathan</span> <span word="Tilly">Tilly</span> <span word="of">of</span> <span word="Harvard">Harvard</span> <span word="Medical">Medical</span> <span word="School">School</span> <span word="and">and</span> <span word="his">his</span> <span word="colleagues">colleagues</span> <span word="discovered">discovered</span> <span word="stem">stem</span> <span word="cells">cells</span> <span word="inmouse">inmouse</span> <span word="ovaries">ovaries</span>. <span word="Since">Since</span> <span word="then">then</span> <span word="it">it</span> <span word="has">has</span> <span word="been">been</span> <span word="shown">shown</span> <span word="that">that</span> <span word="these">these</span> <span word="ovarian">ovarian</span> <span word="stem">stem</span> <span word="cells">cells</span> <span word="can">can</span> <span word="develop">develop</span> <span word="intoeggs">intoeggs</span>, <span word="be">be</span> <span word="fertilised">fertilised</span> <span word="and">and</span> <span word="produce">produce</span> <span word="perfectly">perfectly</span> <span word="healthy">healthy</span> <span word="mouse">mouse</span> <span word="pups">pups</span>. <span word="But">But</span> <span word="researchers">researchers</span> <span word="have">have</span> <span word="beenreluctant">beenreluctant</span> <span word="to">to</span> <span word="believe">believe</span> <span word="that">that</span> <span word="something">something</span> <span word="similar">similar</span> <span word="might">might</span> <span word="be">be</span> <span word="possible">possible</span> <span word="in">in</span> <span word="humans">humans</span>.</p>
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