The right answer is alternative four.
In the excerpt from "A Relay Race to Remember," the expression "he was gliding through the water like a dolphin" injects surprise into the story by making a comparison between that conveys how well Sean performs in he race. The phrase describes that Sean swims as well as a dolphin, meaning that he executes brilliantly at the race.
The rest of the options are not correct because the remark does not develop Malik's character or depicts how he swims, and it is not the end of the story.
