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Which of the following best completes the passage below?
Monarch butterflies, whose average life span is nine months, migrate from the midwestern United States to selected forests outside Mexico City. It takes at least three generations of monarchs to make the journey, so the great-great-grandchildren who finally arrive in the Mexican forests have never been there before. Yet they return to the same trees their forebears left. Scientists theorize that monarchs, like homing pigeons, map their routes according to the earth’s electromagnetic fields. As a first step in testing this theory, lepidopterists plan to install a low-voltage transmitter inside one grove of “butterfly trees” in the Mexican forests. If the butterflies are either especially attracted to the grove with the transmitter or especially repelled by it, lepidopterists will have evidence that______
(A) monarch butterflies have brains, however minuscule
(B) monarch butterflies are sensitive to electricity
(C) low-voltage electricity can affect butterflies, whether positively or adversely
(D) monarchs map their routes according to the earth’s electromagnetic fields
(E) monarchs communicate in intergenerationally via electromagnetic fields
答案B说，butterfly is sensitive to electricity，
而D说，monarchs maps according to earth electromagnetic
D更加迎合科学家的推测，选B是因为文中的实验是 as a first a step？如果真是，真是防不胜防阿 | 
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发表于 2005-6-11 15:05:00
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