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  3. The Migration of the California Grey Whale One of nature’s greatest achievements is the California grey whale. At birth a gr

The Migration of the California Grey Whale One of nature’s greatest achievements is the California grey whale. At birth a gr

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问题                       The Migration of the California Grey Whale
    One of nature’s greatest achievements is the California grey whale. At birth a grey whale calf(小仔) weighs 2,000 pounds and is fourteen feet long. Every day the calf consumes fifty gallons of the mother’s milk and gains fifty pounds of weight. At maturity this whale will weigh 80,000 pounds, be fifty feet long and eat several tons of food each day. The California grey whale spends most of its sixty-year life span on the road.
    Every year thousands of grey whales make the longest migration of any animal, traveling 7,000 miles each way between the Arctic(北极圈)and Baja, California. The grey whales spend the long summer days in their Arctic feeding grounds in the Bering Sea between Alaska and Russia. Unlike a fish, the whale is warm-blooded and must therefore maintain a relatively high internal body temperature. In the cold Arctic waters the grey whale is protected by an outer layer of blubber(鲸脂)which averages six inches in thickness. Other whales such as the Greenland Night whale have been found with a two-foot thick layer of blubber covering their bodies.
    During these summer months in the Arctic the grey whales fatten themselves by consuming enormous quantities of small shrimp-like animals called amphipods (端足目动物). Recent observations of a young grey whale, Gigi II, held in captivity (囚禁) at Sea World in San Diego during 1971 and 1972, suggest that the grey whale feeds by sweeping its enormous head over the bottom. The amphipods on which it feeds are either stirred off the bottom or leap off the bottom to escapee. These animals and the surrounding water are sucked into the whale’s mouth. As the water is expelled from the mouth, it passes through coarse baleen (鲸须) fibres. The small animals are trapped and swallowed.
    In October as the days get shorter and ice begins to form over the Arctic feeding grounds, the California grey whale begins its long journey south to the warm waters of Baja, California. During this three-month long trip the whales traveling in groups stay dose to the shore of North America, swimming both day and night and averaging about 100 miles per day.
    Occasionally the whale will take a look around above the water or "skyhop". Either by beating its tail flukes (尾鳍) rapidly or by resting its tail on the bottom, the whale pushes its upper eight to ten feet of body out of the water and takes a look around. At other times the whale will leap its fifty-foot body almost clear of the water, creating a huge splash as it reenters the water. This "breaching" (跃出水面) may be to dislodge(驱逐)whale lice(虱子) or barnacles (附着甲壳动物) or possibly part of a courtship display.
    During the trip south the grey whales that are sexually mature, at least three years old, and not pregnant already, form mating groups. These groups are composed of three whales, two males and a female. The dominant male couples with the female while the second male is kept busy positioning the two whales on their sides facing each other and keeping them together during the sex act. This is no small job, since each whale can be fifty feet long and weighs forty tons.
    During December and January the grey whales arrive at the warm lagoons(环礁湖)along the coast of Baja, California. The whales swim miles inland along narrow shallow channels. These channels are the breeding grounds of the California grey whale. The calf has been gestating (孕育) in the pregnant female for the last thirteen months, that is, since her last journey south. The expectant cow is aided in the birth of the calf by another female that acts as a midwife (助产士). At birth the calf sinks toward the sea floor. Being a mammal (哺乳动物) the whale must breathe at the surface. The midwife guides the baby whale to the surface for its first gulp of air. The calf then finds its mother’s nipples (乳头) and rich whale milk is forced into its mouth. During the next two months the calf will grow twenty feet and double its weight.
    In March the whales begin their long journey north to the Arctic. The newly-pregnant females leave first, followed by the males and immature females. The last to leave the warm waters of Baja are the females and their calves. The whales arrive at their Arctic feeding ground in June. Many scientists believe that during this entire eight month long, 14,000 mile journey, the California grey whale does not feed at all!
Every October, when the surface of the Arctic ______ is covered with ice, the California grey whales set off on their long journey south to their breeding grounds.
选项
答案feeding grounds
解析 从语法上分析，可判断出应该在of后跟名词作宾语；从意义上分析，可在第四段的第一句中找到答案feeding grounds(饲养场)。
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