The specific defenses of the immune system include a variety of cells that circulate in the blood and that make up organs such as the spleen and thymus. how are the cells of the immune system able to differentiate pathogens from the cells of the body?

a. the cells of pathogens are much smaller than human body cells.
b. pathogens move through the body, while human body cells are stationary.
c. pathogens contain foreign molecules, or antigens, on their outer surface.
d. pathogens release foreign molecules, or antigens, when cells of the immune system approach them.