Question

a protein molecule that the body identifies as foreign, triggering the immune response is a(n)
antibody.
antigen.
thrombocyte.
allergy.

Explanation:

Antigens are foreign - substances, often proteins, that trigger the immune response. Antibodies are produced by the immune system in response to antigens. Thrombocytes are blood cells involved in clotting. An allergy is a hypersensitive immune response.

Answer:

antigen