The correct option is B WBCs
The cells involved in the immune system are white blood cells, or leukocytes, which destroy disease-causing organisms or substances. The two types of leukocytes are phagocytes and lymphocytes. The most common type of phagocyte is the neutrophil, which primarily fights bacteria. The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes form in the bone marrow and either stay there and mature into B cells, or they leave for the thymus gland, where they mature into T cells.