Boreal owls range over a much larger area than do other owls of similar size. Scientists have hypothesized that it is scarcity of prey that leads the owls to range so widely. This hypothesis would be hard to confirm directly, since it is not possible to produce a sufficiently accurate count of the populations of small mammals inhabiting the forests where boreal owls live. Careful study of owl behavior has, however, shown that boreal owls do range over larger areas when they live in regions where food of the sort eaten by small mammals is comparatively sparse. This indicates that the scientists’ hypothesis is not sheer speculation.
In the argument given, the two boldfaced portions play which of the following roles?


The first presents an explanatory hypothesis; the second states the main conclusion of the argument.

The first presents an explanatory hypothesis; the second presents evidence tending to support this hypothesis.

The first presents an explanatory hypothesis; the second presents evidence to support an alternative explanation.

The first describes a position that the argument opposes; the second presents evidence to undermine the support for the position being opposed.

The first describes a position that the argument opposes; the second states the main conclusion of the argument.

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考题讲解

情景：北方猫头鹰比与其相似体型的猫头鹰活动范围要大很多。科学家假设是天敌的缺少导致北方猫头鹰活动范围这么大。这个假设很难被证实，因为很难去得出一个准确的数字：北方猫头鹰生活的地方究竟有多少小型哺乳动物。然而，研究北方猫头鹰的行为发现，当北方猫头鹰生活在小型哺乳动物的食物更少的地方，北方猫头鹰确实活动范围更大。这说明科学家的假设并不是凭空猜测。

推理：第一句是整段话讨论的中心：假设是对or错。第二句是支持主结论（假设不是错的）的。

选项分析：

A选项：第一句是解释性假设；第二句至整段话的主结论：第二句并不是主结论。

B选项：正确。第一句是解释性假设；第二句是支持这个假设的证据：因为主结论是和第一句黑体一致的，所以第二句黑体支持主结论也就是在支持第一句黑体。

C选项：第一句是解释性假设；第二句是支持另外一种解释的证据：第二句是支持第一句的。

D选项：第一句描述了整段话反对的一个观点；第二句削弱了支持被反对的观点的证据：第一句是整段话在讨论对错的观点，且最后的结论是“不是错的”。

E选项：第一句描述了整段话反对的一个观点；第二句陈述了整段话的主结论。

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