The correct option is D Stomach to oesophagous
The cardiac sphincter, a circular muscle between the oesophagus and stomach, closes after food enters the stomach and prevents food from going back up into the oesophagus. In some people, the cardiac sphincter does not function properly or it becomes weakened. This leads to contents from the stomach leaking back into the oesophagus. Stomach acids can irritate the oesophagus and cause symptoms of heartburn. Thus, the correct answer is option D.