Final answer:
The sentence that best illustrates Hooper's comfort in the water describes his serenity, freedom, and ease when diving, supporting the claim effectively.
Step-by-step explanation:
The sentence from the text that best supports the claim that Hooper feels comfortable in the water is: "He felt serene. It was the pervasive sense of freedom and ease that he always felt when he dived." This sentence directly expresses Hooper's comfort and positive emotions associated with being in the water, emphasizing his serenity and the freedom and ease he experiences during a dive. The other sentences provided do not highlight his comfort in the water as explicitly as this choice does.