Final answer:
Saliva, tears, and nasal mucus are biological barriers that help protect the body against pathogens.
Step-by-step explanation:
Saliva, tears, and nasal mucus have in common that they all can be classified as biological barriers. These body fluids serve as a first line of defense against pathogens and provide a physical barrier to prevent entry into the body.
Learn more about Biological barriers in the human body