**Core Concept**
Duodenal ulcers are a type of peptic ulcer disease, characterized by mucosal defects in the duodenum, primarily resulting from an imbalance between mucosal defense mechanisms and aggressive factors, such as gastric acid. This imbalance leads to chronic mucosal damage and ulcer formation.

**Why the Correct Answer is Right**
Gastric acid is a primary aggressive factor in the development of duodenal ulcers. The acidic environment of the duodenum, especially when the mucosal defense mechanisms are impaired, leads to mucosal damage and ulcer formation. Gastric acid secretion is influenced by the vagus nerve, gastrin, and histamine, which are key regulators of acid production.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lysolecithin is a surfactant found in bile and can contribute to the pathogenesis of gallstones, but it is not a primary factor in the development of duodenal ulcers.
* **Option B:** Alcohol abuse can exacerbate existing ulcers and impair mucosal healing, but it is not a direct cause of duodenal ulcers.
* **Option D:** Prostaglandins are actually protective against mucosal damage and are involved in the healing of ulcers. They inhibit gastric acid secretion and promote mucosal defense mechanisms.
* **Option E:** Smoking is a risk factor for peptic ulcer disease, but its primary mechanism is not through the direct development of duodenal ulcers. Smoking impairs mucosal defense mechanisms and increases gastric acid secretion.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the development of duodenal ulcers is often associated with Helicobacter pylori infection, which can lead to chronic inflammation and mucosal damage. Long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) can also contribute to the development of ulcers.

**Correct Answer: C. Gastric acid**