The skin, tears, and stomach acid are part of the body's first line of defense against infection. How do scientists classify these defenses?

A. as specific defenses, because they respond to specific physical or chemical properties of pathogens
B. as weak defenses, because they stop only a small percentage of pathogens that threaten the body
C. as nonspecific defenses, because they bar or stop infections without discriminating pathogens from other agents
D. as barrier defenses, because they act like a wall to stop pathogens from invading

C.as nonspecific defenses, because they bar or stop infections without discriminating pathogens from other agents

Explanation:

The skin, tears and stomach acid are nonspecific defenses and they are some of the examples of the body's first line of defense. Nonspecific defenses are made up of interferons, chemical barriers (e.g. tears and stomach acid), inflammation and physical barrier (e.g. skin).

These nonspecific defenses defend the body from pathogens through their chemical contents in the body fluid or the tissue.

For example, Stomach acid is made of hydrochloric acid (HCl), HCl is potent enough to destroy pathogens that make its way into the stomach through food; this kind of barrier is a chemical barrier.

So also, the skin is a physical barrier which serve as a defense against pathogens.