Which of the following is not a vestigial organ?

The organ that is not considered a vestigial organ is (a) Diaphragm. The diaphragm is a crucial muscle involved in the process of breathing. It contracts and relaxes to facilitate inhalation and exhalation, allowing air to flow into and out of the lungs. Without the diaphragm, proper respiration would not be possible.

On the other hand, both (b) Centriole and (c) Appendix are considered vestigial organs. Centrioles are small, barrel-shaped organelles found in animal cells, and while they play a role in cell division, they are not essential for cell survival in many cell types. Similarly, the appendix is a small pouch-like structure located at the junction of the small and large intestines. While it may have had a digestive function in our evolutionary ancestors, it is now considered vestigial in humans, with its precise function not fully understood.