To solve this problem, we need to identify which structure guards the opening of the hepatopancreatic duct into the duodenum. Let's analyze each option:$\newline \bullet$Option 1: Semilunar valve - These are valves located in the heart, specifically in the aorta and pulmonary artery, and are not related to the hepatopancreatic duct.$\newline \bullet$Option 2: Ileocaecal valve - This valve is located between the ileum and the caecum in the digestive tract and does not guard the hepatopancreatic duct.$\newline \bullet$Option 3: Pyloric sphincter - This sphincter is located between the stomach and the duodenum, controlling the passage of food from the stomach to the small intestine. It is not related to the hepatopancreatic duct.$\newline \bullet$Option 4: Sphincter of Oddi - This is a muscular valve that controls the flow of digestive juices (bile and pancreatic juice) through the hepatopancreatic duct into the duodenum.$\newline$Therefore, the correct answer is Option 4: Sphincter of Oddi, as it guards the opening of the hepatopancreatic duct into the duodenum.