The easiest way to eliminate (A) is to see that P3 doesn’t involve any “empirical disconfirmation” of something. Rather, the author points out how evidence traditionally seen as explained by one hypothesis (adaptation to a high-meat diet) might actually be explained by a different hypothesis (adaptation to cooking). This doesn’t constitute a disconfirmation of one hypothesis, though, because we don’t get any data that’s inconsistent with a hypothesis.

The easiest way to eliminate (B) is to see that P2 doesn’t provide an alternative to a theory described in P1. Rather, P2 provides evidence supporting the author’s theory in P1. P2 provides evidence that humans have biologically adapted to cooking.

The easiest way to eliminate (B) is to see that P2 doesn’t explore a possible objection to the claim the author argues for in P1. Rather, P2 provides evidence supporting the author’s theory in P1. P2 provides evidence that humans have biologically adapted to cooking.

What are the two proposals? That humans are biologically adapted to cooking, and that they’re not? If so, P2 and P3 don’t clarify the difference between those proposals. They describe evidence that might support the hypothesis that humans are biologicaly adapted to cooking.

This is the best answer. Notice that the author begins P2 by noting that important questions “therefore” arise concerning why humans typically can’t survive on raw food. The “therefore” indicates the author believes certain questions are are raised by (implied by) the claim made in P1 that humans are unable to survive on raw-food diets in the wild. “Empirical” in this context means that the questions that are raised involve things that we can observe or measure, such as what’s the correlation between tooth/jaw reduction and cooking practices? And is there a correlation between changes in digestive anatomy and cooking practices? The author explores those questions in P2 and P3.