Explanation: If you read the excerpt the character is in a very difficult situation. He is swimming in high waters and as “he stroke” or swam with his arms he was becoming more slow due to all the physical effort he is putting into. Each kick in the water caused an enormous tension on his ankles. “Emphasized” here refers to “put stress on” because the other options don’t have anything to do with the situation. “Took note of” would mean he knows he’s hurting physically but will ignore the pain, “gave ease to” would mean he would find relief and “used strength for” would mean he’s putting all the strength he’s got to the pain or the ankle.
The sentence should be clear like this: “He recognized that his stroke was slowing as each agonizing kick in the water put stress on his throbbing pain to his ankle”
