Concept:A vestigial structure is a body part that has lost most or all of its original function over the course of evolution.
Explanation:The tailbone, or coccyx, is the small triangular bone at the bottom of the vertebral column in humans.
It is the remnant of a tail that was present in early mammalian ancestors.
Over time, as humans evolved to walk upright, the tail became unnecessary and reduced to this small bone.
Therefore, the tailbone serves little to no function in the modern human body, making it a classic vestigial structure.
Other options like the earlobe, gallbladder, and villus are not considered vestigial in humans.
Answer:C. tailbone