Answer:
B. Pathogen
Step-by-step explanation:
An antibody is a type of protein that is part of the immune systems defense against diseases. Immunaglobin in the most common antibody.
A pathogen is bacteria, virus, etc that causes disease. An example would be Streptococcus, the flu, etc
An antigen is some sort of toxin/foriegn substance that lowers the immune systems responses. An example would be like snake poision or toxic waste.
A lymph node is an organ that kinda looks like a kidney. its part of the immune system and helps absorbe/dispose of sickness, infection, etc. we have them all over our bodies.