Question

which is one part of the immune system that helps protect the body from diseases?
mucus
skeleton
esophagus
fingernails

Explanation:

Mucus is a part of the immune system. It traps pathogens (like bacteria and viruses) and prevents them from entering the body. The skeleton provides structural support, the esophagus is part of the digestive system (for transporting food), and fingernails are mainly for protection of the fingertips (not a key immune - system component).

Answer:

mucus