题目内容：
根据下面内容，回答题 Weknowthatmanyanimalsdonotstayinoneplace．Birds,fishandotheranimalsmovefromoneplacetoanotheratacertaintime．Theymovefordifferentreasons;mostofthemmovetofindfoodmoreeasily,butothersmovetogetawayfromplacethataretoocrowded.
Whencoldweathercomes,manybirdsmovetowarmerplacestofindfood．Somefishesgivebirthinwarmwaterandmovetocoldwatertofeed．Themostfamousmigrationisprobablythemigrationofthefish,whichiscalled"salmon"．Thisfishisborninfreshwaterbutittravelsmanymilestosaltwater．Thereitspendsitslife．Whenitiscold,itreturnstoitsbirthplaceinfreshwater．Thenitgivesbirthanddiesthere．InnorthernEurope,thereisakindofmouse．Theyleavetheirmountainhomeswhentheybecometoocrowded．Theymovedowntothelowland．Sometimestheymoveallthewaytotheseaside,andmanyofthemarekilledwhentheyfallintothesea.
Recently,scientistshavestudiedthemigrationofakindoflobster．Everyyear,whentheseasonofbadweatherarrives,thelobstersgetintoalongtimeandstarttowalkacrosstheflooroftheocean．Nobodyknowswhytheydothis,andnobodyknowswheretheygo.
So,sometimesweknowwhyhumansandanimalsmovefromoneplacetoanother,butatothertimeswedon't．Maybelivingthingsjustliketotravel.
Themajorityofanimalsmigratefor__________ A．place
B．safety
C．food
D．warmth
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