A nurse is caring for an infant who has aganglionic megacolon causing decreased motility of part of the intestine. The nurse should identify this finding of mechanical obstruction as a manifestation of which of the following disorders?

The correct answer is C, Hirschsprung's disease. This condition is characterized by the absence of ganglion cells in the distal colon, leading to decreased motility and mechanical obstruction. Pyloric stenosis (A) involves narrowing of the opening between the stomach and small intestine, not the colon. Encopresis (B) is fecal incontinence unrelated to mechanical obstruction. Enterocolitis (D) is inflammation of the intestines, not a structural issue like Hirschsprung's disease.