Concept:Vestigial structures are remnants of organs or body parts that performed important functions in distant ancestors but have become reduced or non-functional in present-day organisms.
Explanation:In humans, the tail bone, also called the coccyx, is a small triangular bone at the end of the vertebral column.
It is the leftover of a true tail found in many early primates and other mammals.
In modern humans, it does not help in grasping, balance, or locomotion.
Therefore, the tail bone is considered a vestigial structure because it has lost its original function through evolution.
Earlobes, toe bones, and the spleen have clear, active functions in the human body.
Thus, among the given options, the vestigial structure is the tail bone.
Answer:C. tail bone