求高人指点GMAT-Test-C-12, 实在比较不清楚

jojofgasw

12. 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（B）

(E) monarchs communicate in intergenerationally via electromagnetic fields

Why C is not correct? What is the difference between C and B?

nbnhjf

从文章的内容和结构看，之所以要安装这个发射器，是因为研究人员试图要证明，这种蝴蝶的辨识能力和电磁感应有关，因此，B是比较通顺的选项，如果选C，那么结论和目的就不相关了。