Which of the following guards the opening of the hepatopancreatic duct into the duodenum?

The sphincter of Oddi (or hepatopancreatic sphincter) is a muscular valve made up of smooth muscles that control the flow of digestive juices (bile and pancreatic juice) through the ampulla of Vater into the second part of the duodenum by the movement of the muscular wall. It surrounds the end portion of the bile duct and pancreatic duct and hence, called as a hepatopancreatic sphincter.