Answer:
Physical Barriers (P): Skin , Mucus Membranes
Chemical Barriers (C): Stomach Acid , Antimicrobial Peptides
Biological Barriers (B): Gut Flora , Immune Cells
Explanation: It's important to note that these examples are not exclusive to one type of barrier, as they can overlap in their functions. The categorization as physical, chemical, or biological barriers helps to understand different mechanisms that our body employs to defend against pathogens.