Giant ground sloths began disappearing from the Americas about 10,000 years ago, around the time that the last ice age ended, and are now extinct worldwide.
New Belief
The arrival of human beings, not climate change, is what killed off the giant sloths.
Evidence
Humans arrived shortly before the last ice age ended, which is around the same time that giant ground sloths began disappearing from the Americas.
Evaluate
Since we're discussing what the Cause of a certain Phenomenon was, we can use our Curious Fact / Explanation mindset:
Curious Fact What caused the giant sloths to disappear from the Americas about 10,000 years ago as the last ice age was ending?
Author's Explanation The arrival of humans did it.
We always affect/evaluate these arguments in one of two ways: - Alternate Explanations for the Curious Fact - Plausibility of the Author's Explanation
We were already offered an alternate explanation (climate change), so we could assist the anti-causal part of the scientist's argument by picking any answer that makes it sound like "climate change didn't kill the sloths". (Maybe we get evidence that they would happily tolerate the new climate)
More likely on Strengthen questions is that the correct answer adds plausibility to the Author's Explanation.
Is there any evidence that the presence of humans would imperil sloths? Did humans hunt them or displace / ruin the sloths' habitat?
The most classic form to a Causal Strengthener is the old "No Cause, No Effect" answer, so maybe there will be an answer like,
Goal
Look for something that adds plausibility to the idea that the presence of humans would lead to the disappearance of the giant ground sloths (or something that makes it sound like climate change wouldn't have killed off the sloths)