White blood cells, the cells that lack the characteristic red color (imparted by the presence of high amounts of hemoglobin) of red blood cells, have very important immunological functions.
Basophils (B) are the least common of the granulocytes. These are seen in several inflammatory reactions, as exemplified by allergies. They contain anticoagulant heparin, which prevents blood from clotting too quickly. They also have histamine, which dilates blood vessels and enhances blood flow to the tissues. Therefore, option B is incorrect.
Monocytes are a type of white blood cell or lecocytes. It is true that Monocytes become macrophages (A). Macrophages are large phagocytic cells found stationary in tissues or as mobile in blood, targeted to sites of infection.
Lymphocytes have importance in immune response (C). They are a classification of small leucocytes (white blood cell) with a single round nucleus. They are primarily found in the lymphatic system.
Neutrophils phagocytize microbes (D). They are a type of white blood cell. Most of the white blood cells that lead immune responses are neutrophils.
Therefore, options A, C and D are correct.