Which of the following cannot be digested by humans ?

Cellulose

The correct answer is Option (3) –Cellulose

The grass is rich in cellulose, a type of carbohydrate. In ruminants like cattle, deer, etc., bacteria present in rumen helps in digestion of cellulose.

Many animals, including humans, cannot digest cellulose. Animals like horses, rabbit, etc., have a large sac-like structure called Caecum between the oesophagus and the small intestine .

The cellulose of the food is digested here by the action of certain bacteria which are not present in humans.