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A mysterious phenomenon is the ability of over-water migrants to travel on course. Birds, bees, and other species can keep track of time without any sensory cues
Line from the outside world, and such ―biological clocks‖
5 clearly contribute to their ―compass sense.‖ For example, they can use the position of the Sun or stars, along with the time of day, to find north. But compass sense alone cannot explain how birds navigate the ocean: after a flock traveling east is blown far south by a storm, it will
10 assume the proper northeasterly course to compensate. Perhaps, some scientists thought, migrants determine their geographic position on Earth by celestial navigation, almost as human navigators use stars and planets, but this would demand of the animals a fantastic map sense.
15 Researchers now know that some species have a magnetic sense, which might allow migrants to determine their geographic location by detecting variations in the strength of the Earth‘s magnetic field.
Of the following descriptions of migrating
animals, which most strongly suggests that the
animals are depending on magnetic cues to orient
themselves?
(A) Pigeons can properly readjust their course
even when flying long distances through
exceedingly dense fogs.
(B) Bison are able to reach their destination by
passing through a landscape that has
been partially altered by a recent fire.
(C) Elephants are able to find grounds that
some members of the herd have never seen
before.
(D) Swallows are able to return to a given spot
at the same time every year.
(E) Monarch butterflies coming from different
parts of North America are able to arrive
at the same location each winter.
应该就是定位在文章黑体字部分，答案是A,实在看不懂为什么 |
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发表于 2012-5-1 21:50:08
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