I'm going to say B because the other answers just don't seem to make sense.
Answer:
D. Immune response
Explanation:
An immune response is defined as any reaction that occurs within a host when its body recognizes and defends itself against pathogenic microorganisms (e.g., viruses, bacteria, protists, etc) and/or chemical compounds that look to be foreign and harmful to the body. When the number of detected pathogenic microorganisms increases, the immune system in the host responds by producing cells that attack them or by producing proteins (i.e., antibodies) that destroy the harmful substances. A substance capable of triggering an immune response is known as an antigen (e.g., a structural protein of a pathogenic virus). There are two distinct types of immune responses: 1-innate immune responses, where the body mounts a response immediately without requiring a previous contact with the harmful antigen and does not retain a memory of previous responses; and 2- adaptive immune responses that only occur after exposure to an antigen, these responses are slower but they are specific and produce immunological memory.
