题目选项分析

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?

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