**Core Concept**
Ectopic pancreatic tissue is a rare condition where pancreatic tissue is found outside the pancreas. This can occur due to aberrant migration of pancreatic cells during embryonic development. Ectopic pancreatic tissue can sometimes cause symptoms due to its location and function.

**Why the Correct Answer is Right**
The most common site of ectopic pancreatic tissue is the **Meckel's diverticulum**, a congenital diverticulum of the small intestine. This is because the cells that give rise to the pancreas and the cells that give rise to the intestinal lining are derived from a common embryonic layer. When the intestinal lining fails to fully separate from the pancreatic cells, ectopic pancreatic tissue can form in the Meckel's diverticulum. The presence of ectopic pancreatic tissue in the Meckel's diverticulum can sometimes lead to symptoms such as bleeding, obstruction, or pancreatitis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, but we can discuss that ectopic pancreatic tissue can occur in other locations such as the duodenum, stomach, or omentum. However, these locations are less common than the Meckel's diverticulum.
* **Option B:** This option is not provided, but we can discuss that ectopic pancreatic tissue is not typically found in the spleen or liver.
* **Option C:** This option is not provided, but we can discuss that ectopic pancreatic tissue can sometimes cause symptoms due to its location and function, but it is not typically found in the gallbladder.

**Clinical Pearl / High-Yield Fact**
It's worth noting that Meckel's diverticulum is a congenital anomaly that can contain ectopic tissue from all three embryonic layers, including pancreatic tissue. The presence of ectopic pancreatic tissue in the Meckel's diverticulum can sometimes lead to symptoms and can be diagnosed with imaging studies or endoscopy.

**Correct Answer: C. Omentum.