题目内容：
根据以下材料，回答题 Pain
Allofushavefeltpain．Wehavecutourselves．Wehavebeenburned．Orwehavehadheadaches．Someofussufferpainrarely．(46)
Paincantakecompletecontrolofourbodyandmind,makingitimpossibletomoveandeventothink．Yetweneedpain．Withoutit,wewouldnotknowifwehavehurtourselves．Itisourbody'swarningsystem．(47)
Painisthemostcommonreasonwegotoadoctor．Itisthemostcommonreasonwetakemedicines．Untilrecently,however,mostdoctorsknewofonlyafewdrugsthatstoppedsomepains.
(48)Butnewknowledgeabouttheprocessofpainishelpingthemtocontrolpainbetter.
Scientistshavelearnedthatthesenseofpainismadeupofbothchemicalandelectricalsignals．(49)．Scientistshavealsolearnedthatthenervoussystemsendstwodifferentkindsofpainmessagestothebrain:oneveryfast,theotherslow.
Thefirstmessageisthewarningsignal．Itmovesataspeedof30metersasecond．Inlessthanasecond,thebrainunderstandsthatpartofthebodyishurtandhowbadlyitisinjured．(50)Ittellsusnottousetheinjuredpartuntilitheals.
回答(46)题 A．Andothershavepainfulattacksallthetime.
B．Thesesignalstravelfromnervecellsintheinjuredarea,upthespinalcord(脊髓)tothebrain,andbackdownagain.
C．Ittellsusthatweareinjuredandshoulddosomethingaboutit.
D．Theyknewlittleabouttheprocessofpainitself.
E．Theothermessagemovesataspeedofonly30metersasecond.
F．Andtheysendthesecond,slowermessageofpaintothebrain.
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