Question

what is an allergy? the body fighting against itself the body reacting to a foreign substance a foreign substance

Explanation:

An allergy is a condition where the immune system reacts to a foreign substance (allergen) that is typically harmless. The first option describes an autoimmune disorder (body fighting itself), and the third is just the allergen, not the reaction. So the correct description is the body reacting to a foreign substance.

Answer:

The body reacting to a foreign substance (the second option among the given choices, with the text "The body reacting to a foreign substance")