Final answer:
Allergic reaction (C) is the appropriate response, representing an overactive immune response to allergens, which are usually harmless environmental substances.
Step-by-step explanation:
The correct answer to the question about an inappropriate response to a nonpathogenic substance is C. Allergic reaction. An allergic reaction is a type of immune response where the body's immune system overreacts to a substance, known as an allergen, that is normally harmless. In allergies, proteins from the environment such as pollen or pet dander trigger the immune system to produce antibodies.
These antibodies bind to immune cells like mast cells, which release histamine and other inflammatory chemicals upon subsequent exposure to the allergen. This can lead to symptoms ranging from mild discomfort like sneezing and itchy eyes, to severe reactions such as anaphylactic shock, which can be life-threatening without immediate treatment.