**Core Concept**
The triad of vomiting, abdominal distension, and a "string of beads" sign on abdominal X-ray is related to **intestinal obstruction**, which is a mechanical or functional blockage of the intestine. This condition can lead to severe complications if not managed promptly. The "string of beads" sign is characteristic of a specific type of intestinal obstruction.

**Why the Correct Answer is Right**
The correct answer is related to **intussusception**, a condition where a part of the intestine telescopes into another, causing obstruction. The "string of beads" sign is seen due to the presence of air-filled loops of intestine. Intussusception is a common cause of intestinal obstruction in children and can also occur in adults.

**Why Each Wrong Option is Incorrect**
**Option A:** Is incorrect because it does not typically present with the "string of beads" sign.
**Option B:** Is incorrect as it is not commonly associated with this specific triad of symptoms.
**Option D:** Is incorrect because, although it can cause obstruction, it does not typically show the "string of beads" sign.

**Clinical Pearl / High-Yield Fact**
Intussusception is a medical emergency that requires prompt diagnosis and treatment to prevent complications such as bowel ischemia and perforation. The "string of beads" sign is a classic radiographic finding that should raise suspicion for this condition.

**Correct Answer:** D. Intussusception