题目内容：
根据以下材料，回答题
SpacinginAnimals
FlightDistance
Anyobservantpersonhasnoticedthatawildanimalwillallowamanorotherpotentialenemytoapproachonlyuptoagivendistancebeforeitflees."Flightdistance"isthetermsusedforthisinterspeeiesspacing.Asageneralrule,thereisapositiverelationshipbetweenthesizeofananimalanditsflightdistance-thelargertheanimal,thegreaterthedistanceitmustkeepbetweenitselfandtheenemy.Anantelopewillfleewhentheenemyisasmuchasfivehundredyardsaway.Thewalllizard'sflightdistance,ontheotherhand,isaboutsixfeet.Flightisthebasicmeansofsurvivalformobilecreatures.
CriticalDistance
Criticaldistanceapparentlyispresentwhereverandwheneverthereisaflightreaction.
"Criticaldistance"includesthenarrowzoneseparatingflightdistancefromattackdistance.Alioninazoowillfleefromanapproachingmanuntilitmeetsabarrierthatitcannotovercome.Ifthemancontinuestheapproach,hesoonpenetratesthelion'scriticaldistance,atwhichpointthecorneredlionreversesdirectionandbeginsslowlytostalktheman.
SocialDistance
Socialanimalsneedtostayintouchwitheachother.Lossofcontactwiththegroupcanbefatalforavarietyofreasonsincludingexposuretoenemies.Socialdistanceisnotsimplythedistanceatwhichananimalwilllosecontactwithhisgroup--thatis,thedistanceatwhichitcannolongersee,hear,orsmellthegroup--itisratherapsychologicaldistance,oneatwhichtheanimalapparentlybeginstofeelanxiouswhenheexceedsitslimits.Wecanthinkofitasahiddenbandthatcontainsthegroup.
Socialdistancevariesfromspeciestospecies.Itisquiteshort-apparentlyonlyafewyards--amongsomeanimals,andquitelongamongothers.
Socialdistanceisnotalwaysrigidlyfixedbutisdeterminedinpartbythesituation.Whentheyoungofapesandhumansaremobilebutnotyetundercontrolofthemother'svoice,socialdistancemaybethelengthofherreach.Thisisreadilyobservedamongthebaboonsinazoo.
Whenthebabyapproachesacertainpoint,themotherreachesouttoseizetheendofitstailandpullitbacktoher.Whenaddedcontrolisneededbecauseofdanger,socialdistanceshrinks.Toshowthisinman,onehasonlytowatchafamilywithanumberofsmallchildrenholdinghandsastheycrossabusystreet.
WhichofthefollowingisthemostappropriatedefinitionofFlightDistance? A．Distancebetweenanimalsofthesamespeciesbeforefleeing.
B．Distancebetweenlargeandsmallanimalsbeforefleeing.
C．Distancebetweenananimalanditsenemybeforefleeing.
D．Distancebetweencertainanimalspeciesbeforefleeing.
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