The vestigial structures listed in the given responses are tail, ear muscles, and pelvis. However, the one structure that serves a purpose in humans is the ability to raise hair, which causes goosebumps. While this response also mentions the purpose of raising hackles in other animals, the ability to raise hair in humans still serves a purpose in response to cold temperatures, fear, or strong emotions. Therefore, the correct response is "hair raising: goosebumps in humans versus raising hackles to appear larger and aggressive in other animals like cats and monkeys".