Question

which part of the immune system is a physical barrier?
○ skin
○ tears
○ mucus
○ stomach acid

Explanation:

The immune system has physical and chemical barriers. Skin is a physical barrier as it physically blocks pathogens. Tears (contain lysozyme, chemical), mucus (traps pathogens but is more of a mucous membrane - related, and has chemical components), and stomach acid (chemical, due to its acidic nature) are chemical or non - purely physical barriers.

Answer:

A. skin