Final answer:
The best evidence of Hooper feeling comfortable in the water is the sentence stating he felt serene and experienced freedom and ease while diving, reflecting his comfort in the water.
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 conveys a sense of calm and contentment when Hooper is in the water, suggesting a level of comfort and familiarity. It speaks directly to his emotional state and his association of diving with freedom and ease, providing clear evidence of his comfort.