**Core Concept**
The infant's presentation suggests Hirschsprung's disease, a congenital condition characterized by the absence of ganglion cells in the distal colon, leading to functional obstruction.

**Why the Correct Answer is Right**
Hirschsprung's disease is caused by the absence of enteric nervous system ganglion cells in the affected segment of the colon. This results in an inability to relax and pass stool, leading to distension and obstruction. The rectal biopsy is crucial in diagnosing this condition, as it allows for the examination of the rectal mucosa and the presence or absence of ganglion cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not relate to the clinical presentation or the diagnostic findings of Hirschsprung's disease.

**Option B:** This option is incorrect because it refers to a different congenital condition, Meconium Plug Syndrome, which is characterized by a blockage of the rectum due to a plug of meconium, rather than an absence of ganglion cells.

**Option C:** This option is incorrect because it refers to a condition that is not directly related to the clinical presentation or diagnostic findings of Hirschsprung's disease.

**Option D:** This option is incorrect because it does not accurately describe the histopathological findings in Hirschsprung's disease.

**Clinical Pearl / High-Yield Fact**
A key diagnostic feature of Hirschsprung's disease is the absence of ganglion cells in the affected segment of the colon, which can be identified on a rectal biopsy. This condition is a common cause of intestinal obstruction in infants and requires prompt surgical intervention.

**Correct Answer:** C. Aganglionosis of the rectum