阅读理解
下面有一篇短文，每篇短文后有5道题。请根据短文内容，为每题确定1个最佳选项。
HowAnimalsKeepWarm
Manhasinventedwaystokeepwarm, buthowdoanimalsdefendthemselves? Theycannotreasoninthesensethatmancan, butnaturehastakencareoftheanimalkingdombyprovidinganimalswithspecialinstincts. Oneoftheseinstinctsisknownashibernation.
Sleepinglikeadormouseisnotonlyacommonsayingbutisareality. Whenwintercomes, thedormouseandotherhibernatinganimalshavereachedawell-nourishedstate. Theyeatverywellinwarmerdayslayingdownfatinthetissuesoftheirbodiesandduringhibernationthiskeepsthemalive. Safeintheirnests, orburrows, theysleepsoundlyuntilthewarmthofspringarrives.
Bats, tortoises, snakes, eveninsectslikebutterflies, hibernatemoreorlesscompletely. Some, likethesquirrels, sleepduringcoldestweatherbutarerousedbyawarmspell. Duringhibernation, thetemperatureofananimalsbodydropsdrastically. Breathingandheartbeatsalmostcease.
Anotherinstinctivemethodofavoidingintensecoldistoescapebymeansofmigration. Wildswans, seagulls, swallowsandcuckoosareafewoftheverymanykindsofbirdswhichflythousandsofmiles, twiceayear, toavoidcold. Manyanimals. EspeciallythoseoftheArcticregions, havesummerandwinterquarters. TheArcticdeerofNorthAmerica, aswellasthereindeerofEurope, movesouthwardtowardstheforestswhenwinterapproaches. Theyreturntothenorthernareawhenthewarmthofspringbeginstobesensed.
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