The correct option is C Buccal cavity
The fist stage of digestion in human being takes place in the buccal cavity where the chewing and churning of food and mixing of saliva occurs. Saliva consists salivary amylase which acts on the starch molecule of food and converts it into the simple form. The semisolid food with saliva in buccal cavity is called as a bolus. Bolus is then transferred to the stomach with the help of peristaltic movement of the oesophagus. Thus, the correct answer is option C.