【单选题】Manypeoplebelievetheglarefromsnowcausessnow-blindness．Yet,darkglassesornot,theyfindthemselvessufferingfromheadachesandwateringeyes,andevensnow-blindness,whenexposedtoseveralhoursof"snowlight"．TheUnitedStatesArmyhasnowdeterminedthatglarefromsnowdoesnotcausesnow-blindnessintroopsinasnow-coveredcountry．Rather,aman'seyesfrequentlyfindnothingtofocusoninabroadexpanseofbarrensnow-coveredterrain．Sohisgazecontinuallyshiftsandjumpsbackandforthovertheentirelandscapeinsearchofsomethingtolookat．Findingnothing,hourafterhour,theeyesneverstopsearchingandtheeyeballsbecomesoreandtheeyemusclesache．Natureoffsetsthisirritationbyproducingmoreandfluidwhichcoverstheeyeball．Thefluidcoverstheeyeballinincreasingquantityuntilvisionblurs,thenisobserved,andtheresultistotal,eventhoughtemporary,snow-blindness．ExperimentsledtheArmytoasimplemethodofovercomingthisproblem．Scoutsaheadofamainbodyoftroopsaretrainedtoshakesnowfromevergreenbushes,creatingadottedlineastheycrosscompletelysnow-coveredlandscape．Eventhescoutsthemselvesthrowlightweight,darkcoloredobjectsaheadonwhichtheytoocanfocus．Themenfollowingcanthenseesomething．Theirgazeisarrested．Theireyesfocusonabushandhavingfoundsomethingtosee,stopscouringthesnow-blanketedlandscape．Byfocusingtheirattentionononeobjectatatime,themencancrossthesnowwithoutbecominghopelesslysnow-blindorlost．Inthiswaytheproblemofcrossingasolidwhiteterrainisovercome．Snow-blindnessmaybeavoidedby__________A、concentratingtothesolidwhiteterrain
B、searchingforsomethingtolookatinsnow-coveredterrain
C、providingtheeyeswithsomethingtofocuson
D、coveringtheeyeballswithfluid
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