**Core Concept**
Gallstones are the most common cause of acute pancreatitis, accounting for approximately 40-60% of cases. This is due to the obstruction of the pancreatic duct by gallstones, leading to pancreatic enzyme activation and subsequent inflammation.

**Why the Correct Answer is Right**
The obstruction of the pancreatic duct by gallstones causes an increase in pancreatic enzyme activity, leading to autodigestion of the pancreas and inflammation. The common bile duct and pancreatic duct are closely related, and gallstones can easily migrate into the pancreatic duct, causing obstruction. This is often associated with a history of biliary colic or jaundice.

**Why Each Wrong Option is Incorrect**
**Option A:** Alcohol is a common cause of chronic pancreatitis, but it is not the most common cause of acute pancreatitis. While alcohol can cause pancreatitis, it is less common than gallstones.
**Option B:** Hypertriglyceridemia can cause acute pancreatitis, but it is a less common cause than gallstones. High triglyceride levels can cause pancreatitis, but it is often associated with other risk factors such as diabetes or obesity.
**Option C:** Certain medications, such as estrogens and thiazides, can cause pancreatitis, but they are not the most common cause. These medications can cause pancreatitis, but they are less common than gallstones.

**Clinical Pearl / High-Yield Fact**
The "3 Cs" of acute pancreatitis are: gallstones, chronic alcohol use, and hypertriglyceridemia. These are the three most common causes of acute pancreatitis, and identifying them is crucial for diagnosis and treatment.

**Correct Answer: D. Gallstones.**