The structure that serves a purpose in humans from the listed options is the pelvis. In humans, the pelvis supports the upper body and provides attachment for the lower body, while in legless animals like whales and snakes, the pelvis is reduced and nonfunctional.
The other options—hair raising (goosebumps), ear muscles, and the tail bone—are considered vestigial in humans, as they do not serve the same functional purpose as they do in other animals. Goosebumps do not help humans appear larger or more aggressive, ear muscles are not used for hearing, and the tailbone does not function as a balance or communication tool in the way tails do for other animals.