Correct Option: D

The most active phagocytic white blood cells are neutrophils and monocytes. Neutrophil is a type of WBC (leucocyte) that has a lobed nucleus and granular cytoplasm. Neutrophils engulf bacteria and release various substance such as lysozyme and oxidizing agents. Monocyte is the largest form of WBC in vertebrates. It has a kidney shaped nucleus and is actively phagocytic, ingesting bacteria and cell’s debris.