Answer: d. Acids
Step-by-step explanation:
In digestive system the movement of the walls of the organs takes place to facilitate the proper mixing of the food and liquid with digestive juices. The movement of esophagus, intestine and stomach is called as peristalsis.
The acids are present inside the food and also the HCl is released by the stomach the digestive system facilitates their digestion immediately so that they do not harm the stomach wall causing ulcers and prevents acidity.