The correct option is C Erythrocytes
Monocytes are a type of WBCs. Monocytes mature in different types of macrophages.
Lymphocytes are B- cells or T- cells and they have receptors on their surface and are able to bind antigens and thus help the foreign substance to get removed from the body.
Neutrophils are the most abundant type of WBCs. They are phagocytic in nature and are able to engulf foreign substances.
Erythrocytes are red blood cells, that are involved in delivering the oxygen to various tissues.
So, the first three are WBCs that are involved in the immune system, as they help in eliminating various antigens, while the latter is not involved in the immune response.
Thus, the correct answer is option D.