This part of the story's rising action is significant because it heightens the tension and uncertainty faced by the characters. The dialogue reveals their concerns about the potential dangers they may encounter and the implications of their situation, specifically referencing a past perilous encounter at the water park. Reyna's comment about there possibly being "no one left to scream" indicates a dire situation that adds to the suspense and foreboding atmosphere. The characters’ cautious approach suggests that they are moving deeper into a threatening scenario, which is characteristic of rising action as it builds toward the climax of the story.
Therefore, the best answer is that **the plot hits its highest point of action**, as they are confronting unknown dangers that could lead to significant conflict.