**Core Concept**
Meconium ileus is a congenital obstruction of the small intestine caused by an abnormal meconium that is thick and tenacious. This condition is often associated with cystic fibrosis, a genetic disorder affecting the respiratory, digestive, and reproductive systems.

**Why the Correct Answer is Right**
Meconium ileus occurs when the meconium is abnormally thick and sticky due to a deficiency of pancreatic enzymes, particularly trypsin and amylase, which are essential for the proper digestion and hydration of meconium. This leads to an obstruction of the ileum, which can cause severe abdominal pain, vomiting, and constipation in infants. The condition is often diagnosed prenatally or shortly after birth and is a classic sign of cystic fibrosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because meconium plug syndrome is a different condition that occurs when a plug of meconium blocks the intestines, but it is not associated with cystic fibrosis.

**Option B:** This option is incorrect because Hirschsprung's disease is a congenital condition characterized by the absence of ganglion cells in the distal colon, leading to a functional obstruction, but it is not related to meconium ileus.

**Option C:** This option is incorrect because small bowel atresia is a congenital obstruction of the small intestine, but it is not specifically associated with meconium ileus or cystic fibrosis.

**Option D:** This option is incorrect because intussusception is a condition in which a segment of intestine telescopes into another, but it is not related to meconium ileus or cystic fibrosis.

**Clinical Pearl / High-Yield Fact**
Meconium ileus is a classic sign of cystic fibrosis, and its presence should prompt further investigation for this condition, including sweat chloride testing and genetic analysis.

**Correct Answer: A. Meconium plug syndrome is incorrect; the correct answer is actually B. Hirschsprung's disease is incorrect; the correct answer is actually C. Small bowel atresia is incorrect; the correct answer is actually D. Intussusception is incorrect; the correct answer is actually E. Cystic fibrosis.**