Final answer:
The pyloric sphincter opens to allow chyme to enter the small intestine after it leaves the stomach, marking the end of the gastric phase and beginning of the small intestine processing.
Step-by-step explanation:
The pyloric sphincter opens to let chyme enter the small intestine after the food leaves the stomach. Chyme is a thick, semi-liquid mixture of food and digestive juices that forms in the stomach. This process is a part of gastric emptying, where rhythmic mixing waves force about 3 mL of chyme at a time through the pyloric sphincter into the duodenum. The timing of this event is crucial, as a larger release might overwhelm the small intestine's capacity to handle it. Hence, correct answer to the question is 'd) After food leaves the stomach'.
Regarding the statements provided about the digestive system, the false one is 'b. Food enters the large intestine before the small intestine,' as food actually enters the small intestine directly after passing through the stomach.