P3 doesn’t compare evolutionary game theory and classical game theory, which were the two theories introduced in P2. Because (A) doesn’t happen, it can’t be the purpose of P3.

There is no theory that is described in the “first two paragraphs of the passage.” Evolutionary game theory is described in P2, and the traditional theory is described in P1. Because (B) doesn’t happen, it can’t be the purpose of P3.

P3 doesn’t describe an experiment. Riechert didn’t actually go out and test how spiders behave in grassland and riparian habitats. P3 presents what Riechert thinks would happen in each of these habitats.

P3 doesn’t describe a rare phenomenon. In fact, there’s no phenomenon in P3. We don’t know how spiders actually behave in grassland and riparian habitats. P3 presents what Riechert thinks would happen in these habitats.

This best captures the purpose. P3 describes Riechert’s predictions for spider behavior in grassland and riparian habitats. We can use these predictions to assess the validity of evolutionary game theory. If the predictions are confirmed, the theory gets more support. If the spiders don’t behave as predicted, the theory has less support.