Answer: To complete the process of digestion after the food is ingested by mouth.
Explanation:
The food that we eat is ingested by mouth and here the mechanical degradation of food takes place. This breaks down the food into smaller pieces.
Mouth also contains the enzyme that is responsible for the digestion of starch.
Then the food from the mouth reaches the stomach where various types of digestive juices and enzymes are secreted to digested the food.
Hence, mouth and stomach must be near in the digestive system.