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 LACE w:st="on">Mexico CityLACE>. 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，而从题目给出的目的用该是为了验证electromagnetic fields，而不是electricity，我觉得应该是d比较好，我看讨论有些人倾向于c，我觉得c一个是因为缺少monarch的限定，最主要的还是因为electricity而不是electronmagnetic fields。所以我认为d较好。思维有问题吗？难道这二者是一样的？胡涂了，请指出我的毛病所在。谢谢 | 
