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

我觉得c好像更好一点，两者的区别不是很大，怎么回事呢？

there are only slight difference

choice C does not include the word monarchs which means electricity can affect all butterflies, while we just have to prove that it affects monarchs.

我的第一感觉和你一样，就是B和C差不多，可是c选项仔细读起来有歧义，因为低电压对蝴蝶有影响，可正可负

而B选项蝴蝶是主动的，就是他们可以接近，也可以逃开，蝴蝶对电压敏感

有道理，两者的侧重点不同，文中显然想知道的是蝴蝶对电的反应，而不是电对蝴蝶的影响。

C说的是butterflies 而不是monarch butterflies范围发生了变化 所以不应该选这个选项.