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Unit 4 Global warming全球变暖引起北极冰雪融化，这一变化给北极熊赖以生存的家园带来了极大的威胁。
北极熊通常在冰原上养育幼崽,而随着冰的融化，它们待在陆地上的时间被迫加长，吃不到冰面上可以捕捉到的海豹，从而只能以当地猎人捕捉的鲸的残余物为食……这严重影响了它们的生存及繁殖。
晨读晚诵■ n柱预知介作探处上单词注释难句剖析导读诱思Due to climate changes,Arctic ice is breaking up earlier in the spring,and its area is decreasing.This is creating problems for polar bears that make their homes off northern Alaska and in Hudson Bay.Polar bears off Alaska normally hunt and raise their young on ice sheets that float on the ocean.But as the ice has melted,the polar bears have been forced to spend more time on land.There.they have begun to firequent ① beaches,feeding on the remains ② of whales caught by native hunters.For polar bears,this food is less nutritious® than seals that they nonnally catch on ice sheets.The shrinking ice has also forced more polar bears into the ocean.In the past,they only had to swim short distances between ice sheets.But as the ice has shrunk,polar bears have been forced to swim longer and longer distances in the open ocean.This poses ④ asevere danger during rough weather ?and an increasing number ofdrowned polar bears have been observed.In Hudson Bay,the ice breaks up three weeks earlier in the spring now than it did 20 years ago.Polar bears in Hudson Bay fast 5during the summer,waiting for ice to fonn in the fall to hunt.Every year,the summer gets longer,and the bears get skinnier®.This loss affects their ability toreproduce,and already the number of births has dropped by 15percent.Unless the bears can learn to survive these climate changes,these giants of the ice may one day disappear.①frequent /fr'ikwent/ vt常去，常到（某处）②remains /rlmelnz/ 〃•剩余物③nutritious /njutrlfas/ Q0•有营养的®pose /paoz/讥•造成;形成⑤fast /f□: st/ w.绝食©skinny /sklnl/加/・极瘦的;皮包骨的（skinnier为skinny的比较级）This poses a severe danger during rough weather,and an increasing number of drowned polar bears have been observed・译文这在天气恶劣的时候造成严重的危险，而且被发现的溺水的北极熊越来越多。
