**Core Concept**
ERCP (Endoscopic Retrograde Cholangiopancreatography) is a diagnostic and therapeutic procedure used to visualize and treat conditions affecting the bile and pancreatic ducts. The complications of ERCP are multifactorial, involving the biliary and pancreatic systems, as well as the endoscopic technique itself.

**Why the Correct Answer is Right**
The most common complication of ERCP is pancreatitis, which occurs in approximately 3-5% of cases. This is due to the mechanical trauma caused by the cannulation of the pancreatic duct, leading to inflammation and activation of pancreatic enzymes. The release of pancreatic enzymes can cause damage to the pancreatic tissue, leading to pancreatitis. The risk of pancreatitis is increased by factors such as sphincter of Oddi dysfunction, prior pancreatitis, and the use of certain medications.

**Why Each Wrong Option is Incorrect**
**Option A:** Bile duct injury is a serious complication of ERCP, but it is less common than pancreatitis, occurring in approximately 0.5-1.5% of cases.
**Option B:** Sphincter of Oddi dysfunction is a condition that can increase the risk of pancreatitis and other complications after ERCP, but it is not a complication itself.
**Option C:** Cholangitis is an infection of the bile duct that can occur after ERCP, but it is less common than pancreatitis.

**Clinical Pearl / High-Yield Fact**
It is essential for endoscopists to carefully assess the risks and benefits of ERCP and to use prophylactic measures, such as pancreatic duct stenting, to reduce the risk of pancreatitis.

**Correct Answer: C. Cholangitis is an infection of the bile duct that can occur after ERCP, but it is less common than pancreatitis.