B

　　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 significant environmental problem. The shortened hibernation period could actually lead to significant declines in the population of several species.

　　Some of the first concrete evidence of the phenomenon 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. 5 degrees 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. In parts of the United States, chipmunks(花鼠)also skipped the hibernation period. The bears seem to have survived without losing many individuals. The chipmunks, 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 from their winter slumber, their metabolism returns to normal.

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