13．Now scientists believe that global warming affects hibernating animals，causing them to wake up earlier．While this may seem a little concern，it is in fact a serious environmental problem．The shortened hibernation period could actually lead to significant decreases in the population of several species．
Some of the first evidence of the problem came from Colorado，where researchers at the Rocky Mountain Biological Lab have been observing marmot （旱獭） hibernation behavior since the 1970s．In the early days of their studies，marmots generally hibernated several weeks into the month of May．Nowadays，however，temperatures in the area have risen by 2.5degrees Fahrenheit，and the marmots wake up about a month earlier．
At least the marmots are still hibernating．Several other animals have not been hibernating at all recently．Brown bears in the Spanish Cantabrian Mountains did not hibernate last year．Chipmunks （花鼠） in the US and some snakes in Australia also skipped the hibernation period．The bears seem to have survived without losing many individuals．The chipmunks and snakes，however，were not so lucky．Many of the animals died of starvation during the winter．
The problem with animals waking up early，or skipping hibernation altogether，lies with the creatures'metabolism （新陈代谢）．When the animals hibernate，their metabolism drops significantly．The animals'heart rate slows，and they require very little energy to live．When the animals awake in the spring，their metabolism returns to normal．
But while their metabolism may be as active as it was before hibernation，food sources aren't as available as they were before．A marmot may wake up when temperatures get warmer，thinking it's spring，but plants will not have got the amount of sun they need to grow．So until the plants grow，the marmots have no reliable food source．
Many scientists believe the problem will continue to get worse．For many biologists，that's a scary prospect．Terry Root，an animal expert at Stanford University，said，"I do think what we will be facing is the extinction of many species．"
28．What is the viewpoint of the writer？B
A．Global warming will continue to get worse as time goes on．
B．Waking up early in spring may lead to the extinction of some animals．
C．Shortened hibernation will definitely decrease the population of animals．
D．Animals which do not hibernate die of starvation．
29．The writer sets the example of the marmot in order toA．
A．indicate that global warming influences animals'hibernation
B．explain that the weather gets warmer and warmer now
C．show that the weather in the United States is quite different
D．say some animals do not hibernate now due to warm weather
30．Judging from recent observation，which of the following animals suffered the LEAST from shortened hibernation？A
A．Brown bears．
B．Marmots．
C．Some snakes in Australia．
D．Chipmunks in the US．
31．Why can't marmots find enough food when they wake up？D
A．Because there are too many marmots in the wild now．
B．Because more and more animal species skip hibernation now．
C．Because winter days end much earlier than before．
D．Because plants haven't received enough sunlight for spring growth．
分析 本文属于说明文阅读，作者通过这篇文章主要向我们描述了全球变暖带来的连锁反应很多，其中之一就是导致一些冬眠的动物的冬眠期变短，给这些动物带来巨大的影响；
解答 28．B．细节理解题．根据第一段The shortened hibernation period could actually lead to significant decreases in the population of several species．可知冬眠期的缩短导致数量的减少，故选B项．
29．A．细节理解题．根据第二段Nowadays，however，temperatures in the area have risen by 2.5 degreesFahrenheit，and the marmots wake up about a month earlier．可知作者借这个例子来说明全球变暖使得动物的冬眠期减少，故选A项．
30．A．细节理解题．根据第三段提到Brown bears in the Spanish Cantabrian Mountains did not hibernatelast year可知棕熊去年就没有冬眠，可知选A项．
34．D．细节理解题．根据倒数第二段提到but plants will not have got the amount of sun they need to grow．植物没有得到足够的阳光来生长，故选D项．
点评 考察学生的细节理解和推理判断能力，做细节理解题时一定要找到文章中的原句，和题干进行比较，再做出正确的选择．在做推理判断题不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．
