Choose the word which is different from the rest.

The answer is B. Appendix.

A skull is a bony structure that protects the brain. A pelvis is a bony structure that supports the upper body and connects the legs to the spine. A fibula is a long bone in the lower leg. A vertebra is a bony structure that forms the spine. An appendix is a small, finger-shaped organ that projects from the colon.

The appendix is different from the other options because it is not a bone. It is a small, finger-shaped organ that projects from the colon. The appendix is not essential for life, and it can be removed without any serious consequences. However, the appendix can become infected, which can be a serious medical condition.