Most of our foods are complicated chemical structure.
In order to be absorbed and utilized by the body, they
must be broken down into relatively simple molecules.
The process by which the complex food materials are
changed to simple molecules is called digestion.

Epiglottis stands open during breathing, allowing air into the larynx. During swallowing it closes to prevent aspiration, forcing the swallowed liquids or food to go into the esophagus instead. It is thus the structure that diverts passage air into  the trachea and food into the esophagus

• Variables considered with feeding rate and gastric evacuation time includes temperature, season, activity, body size, gut capacity, satiety, and metabolic rate. 
• Gastric emptying rate declines more or less exponentially with time. Larger meals first are digested at a faster rate than small meals and the amount of pepsin and acid produced was somewhat proportional to the degree of distension of the stomach.
•  Stomach mobility often increases with the degree of stomach distension also. Gastric emptying time is approximately 3 - 4 hours.

Beaumont recognized that he had in St. Martin an unusual opportunity to observe digestive processes. Dr. Beaumont began to perform experiments on digestion for the first time using the stomach of St. Martin. He is known as father of gastric physiology.

The correct answer is (d).