Trypanosomes are a group of organisms that share which of the following characteristics?

A) free-living aquatic parasites, round cell, no flagellum
B) intestinal parasites, shelled cell structure with pseudopodia
C) opportunistic parasites, multicellular with paired flagellum and apicoplast
D) obligate parasites, elongated cell with single flagellum and a kinetoplast
E) anaerobic parasites, single cellular structure with cilia