In frog, which one of the following opens into the duodenum?

Options

A. Pancreatic duct
B. Bile duct
C. Hepatic duct
D. Hepato-pancreatic duct

Answer

To determine which structure opens into the duodenum in a frog, we need to analyze the options provided:

1. **Pancreatic Duct**: This duct carries digestive enzymes from the pancreas to the duodenum but does not directly open into it.

2. **Bile Duct**: This duct carries bile from the liver to the duodenum but is not the primary duct that combines with others to enter the duodenum.

3. **Hepatic Duct**: This duct transports bile from the liver but does not open directly into the duodenum.

4. **Hepatopancreatic Duct**: This is a combined duct formed by the merging of the bile duct (from the gallbladder) and the pancreatic duct. It opens directly into the duodenum.

### Step-by-Step Solution:

1. **Identify the Ducts**: Understand the function of each duct listed in the options.
- **Pancreatic Duct**: Transports enzymes from the pancreas.
- **Bile Duct**: Transports bile from the liver.
- **Hepatic Duct**: Transports bile from the liver.
- **Hepatopancreatic Duct**: A combination of the bile duct and pancreatic duct.

2. **Understand the Function of the Hepatopancreatic Duct**:
- The hepatopancreatic duct is formed when the bile duct and pancreatic duct merge.
- This duct is responsible for delivering both bile and pancreatic juices into the duodenum.

3. **Conclusion**: Since the hepatopancreatic duct is the only duct that combines both bile and pancreatic secretions and opens into the duodenum, it is the correct answer.

### Final Answer:
The structure that opens into the duodenum in a frog is the **Hepatopancreatic Duct**.