The correct answer is D.

White blood cells are part of the body's defense against pathogens and tumor surveillance. Some white blood cells, in particular macrophages and neutrophils, are able to phagocytose bacteria and cellular debris. Answer choice A is incorrect because paramecia are members of the ciliate class of protozoa that ingest food through an oral groove that is guided by beating cilia. The cilia directs the food into a food vacuole where it is digested, and waste is exuded through the anal pore. Answer choice B is incorrect because red blood cells do not phagocytose, rather their function is to carry O2 in hemoglobin. Answer choice C is incorrect because hydra are coelenterates that have a mouth/anus common opening. Tentacles help push food into this cavity as this organism is too large to phagocytose. Answer choice E is incorrect because flame cells are the excretory system of flatworms. The cilia that push the waste out of the organism look like a flame.