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  3. Sea otters dwell in the North Pacific. They are the largest of the mustelids, a group which also includes freshwater otters, wea

Sea otters dwell in the North Pacific. They are the largest of the mustelids, a group which also includes freshwater otters, wea

admin2010-07-19  48
问题    Sea otters dwell in the North Pacific. They are the largest of the mustelids, a group which also includes freshwater otters, weasels, and badgers. They are from four to five feet long, and most weigh from 60 to 85 pounds. Large males may weigh 100 pounds or more.
   Unlike most marine mammals, such ms seals or dolphins, sea otters lack a layer of blubber, and therefore have to eat up to 30% of their body weight a day in clams, crabs, fish, octopus, squids, and other delicacies to maintain body heat. Their voracious appetites do not create food shortages, though, because they are picky eaters, each animal preferring only a few food types. Thus no single type of fond source is exhausted. Sea otters play an important environmental role by protecting forests of seaweed called kelp, which provide shelter and nutrients for many species. Certain sea otters feast on invertebrates like sea urchins and abalones that destroy kelp.
   Sea otters eat and sleep while floating on their backs, often on masses of kelp. They seldom come on shore. Sea otters keep warm by means of their luxuriant double-layered fur, the densest among animals. The soft outer fur forms a protective cover that keeps the fine underfur dry. One square inch of underfur contains up to 1 million hairs. Unfortunately, this essential feature almost led to their extinction, as commercial fur hunters drastically reduced their numbers.
   Under government protection, the sea otter population has recovered. While elated by the otters return, scientists are concerned about the California sea otter population growth of 5% a year, lagging behind the 18% a year rate among Alaska otters. Sea otters are extremely sensitive to pollution. In 1989 up to 5,000 sea otters perished when the Exxon Valdez spilled oil in Prince William Sound, Alaska.
Why are scientists concerned about the population of California sea otters according to the passage?
选项 A、It has been growing at too fast a rate.
B、Its growth rate has been steadily decreasing.
C、Its growth rate is not as fast as that of the Alaska sea otters.
D、It has been greatly reduced by oil spills and other forms of pollution.
答案C
解析
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