The carbohydrate which cannot be digested by the human digestive system is

Cellulose is a complex structural polysaccharide found in plant cell walls. The human digestive system lacks the specific enzyme cellulase required to break down the $\beta -1,4\text{-glycosidic}$ linkages present in cellulose, rendering it indigestible as a source of energy, though it acts as vital dietary fiber.