A three year old male child presents with history of constipation and abdominal distension for the last two yrs.The plain radiograph of abdomen reveals fecal matter containing distended bowel loops.A barium enema study done subsequently shows a transition zone at the recto-sigmoid junction with reversal of recto-sigmoid ratio.The most probable diagnosis is:

• A. Anal atresia
• B. Malrotation of the gut
• C. Hirschsprung's disease
• D. Congenital megacolon