The correct option is B Didelphis
Koala, scientific name Didelphis coola, are hindgut fermenters, such that their digestive retention can last for 100 hours because of the presence of extremely long caecum. Thus, only 10% of the animal's energy is obtained from fermentation. Since, the koala gains a low amount of energy from its diet, its metabolic rate is half that of a typical mammal. The koala passing relatively dry faecal pellets high in undigested fibre and thereby stores water in the caecum.