大全GMAT TestC-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

(E) monarchs communicate in intergenerationally via electromagnetic fields

做题时选了B.回头再看觉得C好象也可以.答案是B.为什么B就比C好呢?

I think, the key is "affect".  The test shows monarch butterflies can "feel" low-voltage electricity so that they can be "attracted" or "repelled". 

而“affect”就难说了，如果butterflies不能感知信号，却会受到影响，例如寿命减短，飞行紊乱等等，不见得会  be "attracted" or "repelled".  因此试验能够证明感知，不能证明影响。

虽然“sensitive ”也能够表达容易受到影响的意思，但反过来“affect”就不能表达存在感知能力的意思。这方面就没必要深究语义了，毕竟是逻辑分析题。