Manypeoplebelievetheglarefromsnowcausessnow-blindness．Yet,darkglassesornot,theyfindthemselvessufferingfromheadachesandwateringeyes,andevensnow-blindness,whenexposedtoseveralhoursof"snowlight"． TheUnitedStatesArmyhasnowdeterminedthatglarefromsnowdoesnotcausesnow- blindnessintroopsinasnow-coveredcountry．Rather,aman'seyesfrequentlyfindnothingtofocusoninabroadexpanseofbarrensnow-coveredterrain．Sohisgazecontinuallyshiftsandjumpsbackandforthovertheentirelandscapeinsearchofsomethingtolookat．Findingnothing,hourafterhour,theeyesneverstopsearchingandtheeyeballsbecomesoreandtheeyemusclesache．Natureoffsetsthisirritationbyproducingmoreandfluidwhichcoverstheeyeball．Thefluidcoverstheeyeballinincreasingquantityuntilvisionblurs,thenisobserved,andtheresultis total,eventhoughtemporary,snow-blindness． ExperimentsledtheArmytoasimplemethodofovercomingthisproblem．Scoutsaheadofamainbodyoftroopsaretrainedtoshakesnowfromevergreenbushes,creatingadottedlineastheycrosscompletelysnow-coveredlandscape．Eventhescoutsthemselvesthrowlightweight,darkcoloredobjectsaheadonwhichtheytoocanfocus．Themenfollowingcanthenseesomething．Theirgazeisarrested．Theireyesfocusonabushandhavingfoundsomethingtosee,stopscouringthesnow-blanketedlandscape．Byfocusingtheirattentionononeobjectatatime,themencancrossthesnowwithoutbecominghopelesslysnow-blindorlost．Inthiswaytheproblemofcrossingasolidwhiteterrainisovercome． ?Thescoutsshakesnowfromevergreenbushesinorderto__________．
A.give the men behind something to see
B.beautify the landscape
C.warm themselves in the cold
D.prevent the men behind from losing their way
正确答案是A