## **Core Concept**
The most common site for peptic ulcers in the duodenum is closely related to the areas exposed to acidic gastric contents. Duodenal ulcers typically occur in the first part of the duodenum, which is the portion immediately following the pylorus.

## **Why the Correct Answer is Right**
The correct answer, **D. First part of duodenum, near the pylorus**, is right because the first part of the duodenum is most exposed to acidic gastric contents. This area is prone to ulcer formation due to the high concentration of gastric acid and the presence of **gastric secretory cells**. The proximity to the pylorus, where the stomach empties into the duodenum, subjects this area to direct exposure to stomach acid.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify a location. Without a specific location, it's impossible to assess its accuracy regarding the most common site for peptic ulcers in the duodenum.
- **Option B:** This option is incorrect because the second part of the duodenum, while it can be a site for ulcers (especially those related to specific conditions like Zollinger-Ellison syndrome), is not the most common site for typical peptic ulcers.
- **Option C:** This option is incorrect because the third part of the duodenum is less commonly associated with peptic ulcer disease compared to the first part.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **duodenal ulcers are more common in the first part of the duodenum, near the pylorus**. This is a high-yield fact because understanding the typical locations of peptic ulcers aids in diagnosis and management. For example, ulcers in this location are more likely to cause gastric outlet obstruction.

## **Correct Answer:** D. First part of duodenum, near the pylorus.