Final answer:
Food enters the stomach through the cardiac sphincter, not the pyloric sphincter which regulates the passage of chyme into the duodenum. The correct answer is D. In the cardiac sphincter.
Step-by-step explanation:
Food enters the stomach via the cardiac sphincter, which is the opening between the esophagus and the stomach. The pyloric sphincter is, on the contrary, the muscular valve that separates the stomach from the small intestine and regulates the passage of chyme into the duodenum, not the site where food actually enters the stomach. The correct answer to the student's question is D. In the cardiac sphincter.
The fundus of the stomach mentioned as an option, is not the entrance but rather a dome-shaped section involved in temporarily storing undigested food and gases released during digestion. The duodenum is the first part of the small intestine where chyme is mixed with bile and pancreatic juices, so it's neither the site where food enters the stomach.