Wrong trigger. We don’t know which method trains dogs quicker. Also, the likelihood of an owner using a stimulus is irrelevant in determining which stimulus owners should use.

This is irrelevant at best, since either stimulus could be given equally often. However, this could even potentially help solve treat-training’s problem, which would undermine the author’s conclusion.

This could justify the use of either method, so it would fail to justify the author’s claim that verbal training should be used instead of treat-training.

The support establishes that treats can’t be supplied in every situation, whereas verbal commands presumably can be. Given this, (D) helps justify the author’s claim that verbal training should be preferred.

Wrong trigger. Treat-training “appears to be an effective training method”, so this principle wouldn’t justify the conclusion that verbal training should be used instead.