Final answer:
The correct answer is A. Lymph nodes are bean-shaped organs situated throughout the body that serve as meeting places for lymphocytes circulating in the blood and antigens brought from sites of infection. The lymph nodes contain germinal centers rich in B and T lymphocytes, as well as macrophages and dendritic cells for antigen presentation.
Step-by-step explanation:
The correct answer is A. Lymph node.
Lymph nodes are bean-shaped organs situated throughout the body that serve as meeting places for lymphocytes circulating in the blood and antigens brought from sites of infection. Lymphocytes encounter these antigens as lymph passes through the lymph nodes. The lymph nodes contain germinal centers rich in B and T lymphocytes, as well as macrophages and dendritic cells for antigen presentation.