如果告诉你下面这道（推断）题：

Of the following descriptions of migrating animals, which most strongly suggests that the animals are depending on magnetic cues to orient themselves?

(A) Pigeons can properly readjust their course even when flying long distances through exceedingly dense fogs.

(B) Bison are able to reach their destination by passing through a landscape that has been partially altered by a recent fire.

(C) Elephants are able to find grounds that some members of the herd have never seen before.

(D) Swallows are able to return to a given spot at the same time every year.

(E) Monarch butterflies coming from different parts of North America are able to arrive at the same location each winter.

答案的依据在这一小段文字（63 words，阅读篇章中的截选）中：

Perhaps, some scientists thought, migrants determine their geographic position on Earth by celestial navigation, almost as human navigators use stars and planets, but this would demand of the animals a fantastic map sense. Researchers now know that some species have a magnetic sense, which might allow migrants to determine their geographic location by detecting variations in the strength of the Earth’s magnetic field.

你能不能快速排除选项（D）和（E）?

你能不能快速快速找出选项（A）、（B）、（C）的关键区别？而后进一步确定答案？

我们来看看怎么加工这63个词的一小段文字，首先浓缩信息到关键：

Scientists 原来的想法是 celestial navigation （星体导航模式），如同人类用stars and planets来导航。Researchers现在知道 a magnetic sense （磁场感），即通过感知磁场强弱的变化，来导航。

然后，我们发现 celestial navigation 与 a magnetic sense 的关键区别：

celestial navigation （星体导航模式）需要观察星体的位置，那么，观察是需要视觉、可视信息以及有利于视觉观察的外部条件的。a magnetic sense （磁场感）是通过感知磁场强弱的变化，那么，就是有感觉、心里有数就行。

找到这个关键，我们可以快速排除选项（D）和（E）。因为对于这两个选项中所述的情况，我们根本无法判断 swallows 和 butterflies 究竟是靠什么导航的，可能靠视觉，可能靠磁场、还可能靠生物自带的声纳系统呢，总之我们全然不知究竟靠什么。于是完全不符合题目要我们去找的靠 magnetic cues 导航。