Explanation
D: Rumen is not a vestigial organ. The rumen is a large fermentation chamber present in the digestive tract of ruminants, such as cattle, sheep, and deer, that is responsible for the breakdown of cellulose from plant material. It is a functional organ and is essential for the animal's survival.
On the other hand, the vermiform appendix, pinna of ear, and molars are all considered vestigial organs, as they have lost their original function or have reduced functionality over time due to evolution. The vermiform appendix is a small, finger-like projection located at the junction of the small and large intestines, and its function in humans is still unclear. The pinna of ear in humans has lost its function in directional hearing and is now mainly a cosmetic feature. The molars in humans are remnants of teeth that were once used to grind and chew tough plant material, but their reduced size and functionality suggest that they are no longer necessary for survival.
