Answer: B. antigens
Step-by-step explanation:
The antigens are the protein molecules which are found on the surface of the pathogens. They are responsible for initiating the immune response in the host body. As the result of invasion of the body by the foreign antigens the body produces specialized proteins which are called as antibodies to fight against the disease causing pathogens.
On the basis of the above description, proteins that tag pathogens for destruction by the immune cells are called as antigens.