. Whichof the following best completes the passage below? Monarch butterflies, whose average lifespan is nine months, migrate from the midwestern United States to selected forests outside Mexico City
. It takes at least threegenerations of monarchs to make the journey, so the great-great-grandchildrenwho finally arrive in the Mexican forests have never been there before. Yetthey return to the same trees their forebears left. Scientists theorize thatmonarchs, like homing pigeons, map their routes according to the earth’selectromagnetic fields. As a first step in testing this theory, lepidopteristsplan to install a low-voltage transmitter inside one grove of “butterfly trees”in the Mexican forests. If the butterflies are either especially attracted tothe grove with the transmitter or especially repelled by it, lepidopteristswill have evidence that______(A) monarchbutterflies have brains, however minuscule (B) monarchbutterflies are sensitive to electricity (C) low-voltageelectricity can affect butterflies, whether positively or adversely (D) monarchs maptheir routes according to the earth’s electromagnetic fields（B） (E) monarchscommunicate in intergenerationally via electromagnetic fields
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发表于 2010-4-1 14:20:31
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