A
In one of the world's most forbidding environments, polar bears spend their summers wandering the Arctic on large pieces of floating ice.They drift for hundreds of miles, finding mates, hunting for seals, and fattening themselves up for the winter.Without the floating ice, the world's largest bears could not survive.Yet at this moment, the polar bears' Arctic habitat is melting away because of global warming.Over the past three decades, more than a million square miles of floating ice has disappeared.
Scientists predict that, if the current rate of global warming continues, most, if not all, of the bears' floating ice will be gone by 2100.As a result, the world's polar bears could face global extinction by the end of this century.
Already, the ice on the southern edge of the polar bears' range is melting about three weeks earlier than in the past.The loss of those weeks leaves the bears less tune to hunt, eat and store up fat.Once the ice melts, the bears must fast (禁食) for up to eight months on land until the floating ice returns.As a result of early melting, there has been a 14 percent decline in the Hudson Bay polar bear population over the past ten years — a decline clearly caused by global warming.
Besides, a growing number of polar bears may be drowning as they are forced to swim more often, and for longer distances, in search of ice sheets.According to a report by the US Minerals Management Service, researchers observed four dead polar bears floating 60 miles off Alaska in September and it was likely that many other bears swimming far off the shore also drowned.
Scientists have concluded that the worldwide population of about 20,000 polar bears is likely to shrink by more than 30 percent in the next 35 to 50 years alone.
语篇解读：本文是一篇说明文。文章主要描述了由于气候变暖，造成北极熊的栖息地的冰大量融化，进而造成北极熊数量大量下降，面临灭绝的情况。
1．What is the main idea of the passage?
A．Polar bears can't die out in the next century.
B．The happy summer of polar bears is disappearing.
C．Continuous global warming will cause the extinction of polar bears.
D．More and more dead polar bears will be found off the coast of Alaska.
解析：选C 主旨大意题。根据第二段“Scientists predict that, if the current rate of global warming continues, most, if not all, of the bears' floating ice will be gone by 2100.As a result, the world's polar bears could face global extinction by the end of this century.”可知，如果全球气候持续变暖的话，北极熊的家园就会消失，它们也会濒临灭绝，因此选C。
2．Why do polar bears drift for hundreds of miles?
A．To fatten themselves for the autumn to live longer.
B．To find more floating ice, mates and better seals.
C．To escape from global warming to survive the winter.
D．To hunt for food and store up fat to live through the winter.
解析：选D 细节理解题。根据第一段的“They drift for hundreds of miles, finding mates, hunting for seals, and fattening themselves up for the winter.”可知，这些北极熊游荡几百英里，寻找配偶，捕食海豹，储存脂肪过冬，故选D。A项中的“for the autumn”，B项中的“more floating ice”，C项的“escape from global warming”与原文的信息不一致。
3．What can we know from the passage?
A．Polar bears can also find food on land and escape from death.
B．The earlier the ice melts, the better life polar bears will have.
C．There will be only about 20,000 polar bears in 35 to 50 years.
D．Drowning is one reason for the decline of polar bears' population.
解析：选D 推理判断题。根据倒数第二段的“Besides, a growing number of polar bears may be drowning as they are forced to swim more often, and for longer distances, in search of ice sheets.”可知，淹死是造成北极熊数量下降的一个原因。A项与文章中的“the bears must fast (禁食) for up to eight months on land”矛盾，B项的描述与文章意义矛盾，其中的better应该是worse。C项中35到50年后有20 000只北极熊错误。
4．What is the writer's attitude to polar bears' extinction?
A．Objective. B．Subjective.
C．Optimistic. D．Doubtful.
解析：选A 推理判断题。本文作者只是根据科学家们的研究，呈现了北极熊濒临灭绝的处境，以及造成这一现象的原因等，态度是客观的，因此选A。B项“主观的”，作者并没有表达自己的主观看法，C项“乐观的”，这与本文的整体思想矛盾，D项“怀疑的”，没有信息依据。
