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  3. Among the species of seabirds that use the windswept cliffs of the Atlantic coast of Canada in the summer to mate, lay eggs, and

Among the species of seabirds that use the windswept cliffs of the Atlantic coast of Canada in the summer to mate, lay eggs, and

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问题     Among the species of seabirds that use the windswept cliffs of the Atlantic coast of Canada in the summer to mate, lay eggs, and rear their young are common murres, Atlantic puffins, black-legged kittiwakes, and northern gannets. Of all the birds on these cliffs, the black-legged kittiwake gull is the best suited for nesting on narrow ledges. Although its nesting habits are similar to those of gulls that nest on flat ground, there are a number of important differences related to the cliff-nesting habit.
    The advantage of nesting on cliffs is the immunity it gives from foxes, which cannot scale the sheer rocks, and from ravens and other species of gulls, which have difficulty in landing on narrow ledges to steal eggs. This immunity has been followed by a relaxation of the defenses, and kittiwakes do not react to predators nearly as fiercely as do ground-nesting gulls. A colony of Bonaparte’s gulls responds to the appearance of a predatory herring gull by flying up as a group with a clamor of alarm calls, followed by concerted mobbing, but kittiwakes simply ignore herring gulls, since they pose little threat to nests on cliffs. Neither do kittiwakes attempt to conceal their nest. Most gulls keep the nest area clear of droppings, and remove empty eggshells after the chicks have hatched, so that the location of the nest is not given away. Kittiwakes defecate over the edge of the nest, which keeps it clean, but this practice, as well as their tendency to leave the nest littered with eggshells, makes its location very conspicuous.
    On the other hand, nesting on a narrow ledge has its own peculiar problems, and kittiwake behavior has become adapted to overcome them. The female kittiwake sits when mating, whereas other gulls stand, so the pair will not overbalance and fall off the ledge. The nest is a deep cup, made of mud or seaweed, to hold the eggs safely, compared with the shallow scrape of other gulls, and the chicks are remarkably immobile until fully grown. They do not run from their nests when approached, and if they should come near to the cliff edge, they instinctively turn back.
Why does the author mention the Bonaparte’s gulls in the second paragraph?
选项 A、To suggest that different groups of gulls react differently to potential gulls.
B、To emphasize that Bonaparte’s gulls are more aggressive than other gulls.
C、To show a contrast with kittiwakes’ loose defense against predators.
D、To point out that all gulls react to predators fiercely.
答案C
解析 推断题。第二段提到“A colony of Bonaparte’s gulls responds to the appearance of a predatory herring gull by flying up as a group with a clamor of alarm calls，followed by concerted mobbing，but kittiwakes simply ignore herring gulls，since they pose little threat to nests on cliffs”即当猎食者银鸥出现在波拿马海鸥的聚集地时，波拿马海鸥会结队飞起并发出嘈杂的警报声，但是三趾鸥却忽视银鸥。二者形成了对比。故本题选C。
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