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

Cellulose is a structural polysaccharide found in the cell walls of plants. The human digestive tract is incapable of breaking down cellulose because it does not secrete the enzyme cellulase, which is required to hydrolyze its specific $\beta \text{-}1,4\text{-glycosidic}$ linkages. Conversely, starch, glycogen, and glucose are readily processed or absorbed by the human body.