**Core Concept**
Pyloric stenosis in infants is a condition characterized by the narrowing of the pyloric channel, leading to gastric outlet obstruction. This results in a range of clinical features that are essential to recognize in order to provide prompt treatment.

**Why the Correct Answer is Right**
The classic triad of symptoms in pyloric stenosis includes **projecting, non-tender epigastric mass**, **persistent and projectile vomiting**, and **hunger following vomiting**. The vomiting is typically forceful and projectile, often described as "coffee ground" in appearance due to the action of gastric acid on the vomit. This symptom complex is highly suggestive of pyloric stenosis and necessitates further investigation.

**Why Each Wrong Option is Incorrect**
**Option A:** While **abdominal distension** can be seen in pyloric stenosis, it is not a specific or diagnostic feature. It can occur due to accumulation of food in the stomach and can be seen in other conditions as well.

**Option B:** **Weight loss** is a common feature of pyloric stenosis due to persistent vomiting and decreased oral intake. It is a critical aspect of the clinical presentation and should prompt further investigation.

**Option C:** **Constipation** is not a typical feature of pyloric stenosis. While infants may experience some delay in bowel movements, it is not a characteristic symptom of this condition.

**Clinical Pearl / High-Yield Fact**
In infants with suspected pyloric stenosis, the **Ultrasound** is a highly sensitive and specific diagnostic tool, often revealing a **thickened pyloric muscle and a narrowed pyloric channel**.

**Correct Answer: A. Abdominal distension.**