The digestive system includes the alimentary canal or gastrointestinal canal. The alimentary canal includes the buccal cavity, esophagus, stomach, small and large intestine, and digestive glands.
Digestion of food starts from the mouth where teeth with the help of the tongue and enzymes present in the saliva changes ingested food into a bolus.
Bolus through its passage from the esophagus passes down into the stomach where gastric cells with their secretions partially digested food and change into chyme.
Chyme passes down into the small intestine (duodenum). Duodenum receives bile juice and pancreatic juice, which neutralizes the acidity of the food as stomach cells secrete hydrochloric acid for enzymes to work on it, resulting in acidic chyme. After neutralizing the undigested food gets passed down into the ileum where complete digestion takes place and food gets absorbed into lymph and blood vessels.
So, digestion of food is completed in the ileum.
So, The correct option is B (Ileum).