B) beetles. C) cottonwood
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D) whitebark pi
The main purpose of the passage is to
A) discuss an ecological phenomenon.
B) analyze a scientific experiment.
C) resolve an environmental debate.
D) draw attention to a historic discovery.

The question is incomplete and the full version can be found online.  

A) discuss an ecological phenomenon.

Explanation:

The question refers to the article titled “Yellowstone Wolves Boost Berry Diet for Grizzlies, Study Says.”

The main purpose of the passage is to discuss the ecological effects of the return of a top predator into an ecosystem. Such is the case of the reintroduction of the gray wolf into Yellowstone National Park, which had the unexpected effect of boosting an important food source for the grizzly bear. The passage is not meant to analyze a scientific experiment, nor to resolve an environmental debate or draw attention to a historic discovery.

"a" because he is appealing to logic as oppose to appealing to the audience's emotions.

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