Passage Summary: During the rainy season, bonobos swallow certain rough leaves whole, and since these leaves help kill worms, researchers think the apes are using them as medicine.

Conclusion: Bonobos likely eat rough Manniophyton fulvum leaves specifically for their medicinal benefits in clearing out parasites.

Reasoning: The leaves are rough-surfaced, swallowed whole during the rainy season, and their ingestion helps eliminate gastrointestinal worms.

Analysis: The argument makes a causal leap from 'this action has a benefit' to 'this action is done because of that benefit.' To strengthen this, we need to rule out other reasons for eating the leaves or show that the bonobos only do this when they actually have worms. Look for an answer that connects the behavior specifically to the presence of the parasites or shows the leaves aren't eaten for nutritional value.