**Core Concept**
Zollinger-Ellison syndrome (ZES) is a rare disorder characterized by excessive gastric acid secretion due to high levels of gastrin, a peptide hormone produced by a gastrin-producing tumor, usually a gastrinoma. This leads to severe peptic ulcer disease and diarrhea.

**Why the Correct Answer is Right**
The triad of Zollinger-Ellison syndrome includes severe peptic ulcer disease, diarrhea, and gastric hypersecretion. The high levels of gastrin stimulate the parietal cells in the stomach to release excessive amounts of gastric acid, leading to peptic ulcers and diarrhea. The gastrin-producing tumor, usually a gastrinoma, is often located in the duodenum or pancreas.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not describe the classic triad of Zollinger-Ellison syndrome. While abdominal pain is a symptom of ZES, it is not part of the original triad.
**Option B:** This option is incorrect because it is a symptom of Zollinger-Ellison syndrome, but it is not part of the original triad. Weight loss is a common symptom of ZES, but it is not a defining feature of the syndrome.
**Option C:** This option is incorrect because it does not accurately describe the triad of Zollinger-Ellison syndrome. While gastric hypersecretion is a key feature of ZES, the original triad also includes severe peptic ulcer disease and diarrhea.

**Clinical Pearl / High-Yield Fact**
To remember the classic triad of Zollinger-Ellison syndrome, use the mnemonic "PUD-D-GH": Peptic Ulcer Disease, Diarrhea, and Gastric Hypersecretion.

**Correct Answer: D. Gastric hypersecretion, peptic ulcer disease, and diarrhea.**