**Core Concept**
Antral obstruction refers to the blockage of the antrum, a part of the stomach, which can lead to vomiting. This condition can be caused by various factors such as gastritis, ulcers, or tumors. The antrum is a muscular region that receives partially digested food from the pyloric canal and prepares it for further digestion in the small intestine.

**Why the Correct Answer is Right**
Antral obstruction typically presents with symptoms such as vomiting, abdominal pain, and weight loss. The vomiting in antral obstruction is usually projectile and bilious, indicating that the obstruction is located beyond the pyloric sphincter. This is because the pyloric sphincter normally prevents the entry of bile and pancreatic juices into the stomach. When the antrum is obstructed, these juices can flow into the stomach, causing the characteristic projectile and bilious vomiting.

**Why Each Wrong Option is Incorrect**
**Option A:** Gastric outlet obstruction is a condition where the pyloric canal is blocked, leading to vomiting. This is a characteristic feature of antral obstruction, so option A is incorrect.
**Option B:** Nausea and vomiting can be present in antral obstruction, but the presence of epigastric pain is not a distinguishing feature.
**Option C:** Weight loss is a common feature of antral obstruction due to malnutrition and dehydration.

**Clinical Pearl / High-Yield Fact**
Antral obstruction can be differentiated from other conditions such as gastritis or peptic ulcer disease by the presence of bilious vomiting and the absence of blood in the vomit.

**Correct Answer: D. Weight gain**