大全-C-12

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

正确答案是B,偶选D。以前有帖子讨论过，但仍不太清楚，明明题中和电磁场有关，答案中却sensitive to electricity。用这是试验的第一步来推理未免太牵强。

low-voltage transmitter 指什么呢？莫非这是解题的关键？

实验只是证明monarchs butterfiles与low-voltage transmitter产生电流的关系，并没有说明这种设备与地球电磁场有必然的联系（当然，如果文章在提供两者类似的论据的话，就可以安全的选D了）

供参考。

文章的前半部分只是在提供背景知识。因为有了那个推理，所以科学家采取了一个试验，就试验的本身来说，其证明的只是蝴蝶对电流有反应，仅此而已。

填空题要注意要求你complete的是一个句子还是要求你结合前文内容。

整个题目只是一篇科学论文的一部分，整篇论文应该是在讲monarchsmap their routes according to the earth’s electromagnetic fields. 但这道题只是讲了试验的第一步，在第一步还没涉及到earth’s electromagnetic fields。

说点题外话，曾做过一篇阅读，好像是gre的，讲的一种鱼，具有和这道题中的butterfly同样的能力，这就是ETS啊，^_^