This compares proportions, but we need to compare absolute quantities. How much solanine is actually left over in a peeled wild potato, and how does that compare to an unpeeled domesticated one? (A) doesn’t answer either of those questions.

This only tells us about the poison content of wild potato skin, which is irrelevant. We need to know the amount of solanine left over in a wild potato without skin, and how that compares to the amount in a domesticated potato with skin. (B) ignores both sides of the comparison.

This compares the solanine content of a peeled wild potato and a same-size unpeeled domesticated one, and confirms that the wild potato comes in at the same amount of solanine or less. So we can conclude that peeled wild potatoes are indeed at least as safe.

This ignores wild potatoes, so it can’t help us reach the comparison in the conclusion. The fact that solanine is the only poison in domesticated potatoes doesn’t tell us how much poison is in a peeled wild potato, or how that compares to the poison in a domesticated potato.

Irrelevant. The conclusion is only about wild and domesticated potatoes of the same size.