**Core Concept**
A contrast enema is a diagnostic and therapeutic procedure used to visualize the intestines and relieve obstruction in infants. The presence of bile in the emesis and abdominal distension in a one-day-old infant suggests an intestinal obstruction.

**Why the Correct Answer is Right**
The findings of bilious emesis and abdominal distension in a neonate are highly suggestive of an intestinal obstruction. A contrast enema can help identify the level and cause of the obstruction. In this case, the most likely diagnosis is **Intussusception**, a condition where a part of the intestine telescopes into another part, causing obstruction and potentially leading to ischemia.

The correct answer is Intussusception because it is a common cause of intestinal obstruction in infants, and a contrast enema can help diagnose and treat this condition by reducing the intussusception and relieving the obstruction.

**Why Each Wrong Option is Incorrect**
* **Option A:** Meconium Ileus is a condition that occurs in newborns with cystic fibrosis, but it typically presents with a distal intestinal obstruction and a characteristic "ground glass" appearance on abdominal radiographs, which is not mentioned in the scenario.
* **Option B:** Duodenal Atresia is a congenital obstruction of the duodenum, but it typically presents with bilious vomiting and a characteristic "double bubble" sign on abdominal radiographs, which is not mentioned in the scenario.
* **Option D:** Hirschsprung's Disease is a congenital condition characterized by the absence of ganglion cells in the distal colon, leading to a functional obstruction. However, it typically presents with a history of delayed passage of meconium and abdominal distension, which is not mentioned in the scenario.

**Clinical Pearl / High-Yield Fact**
In infants with bilious emesis and abdominal distension, a contrast enema should be performed promptly to diagnose and treat intestinal obstruction, especially in the setting of a known or suspected case of Intussusception.

**Correct Answer: C. Intussusception**