This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
Toxic megacolon is seen in – 
Select and explain. 
A. Chronic nonspecific ulcerative colititis, B. Crohn's disease, C. Colonic diverticulosis, D. Hamartomatous polyp
A: Chronic nonspecific ulcerative colititis
Answer: A: Chronic nonspecific ulcerative colititis 
Explanation: Features of UC 

Ulcerative colitis involves the rectum and extends proximally.
In severe cases, entire colon may be involved Pancolitis.
It is a disease of continuity, and skip lesions are not found.
In some patients, distal ileum may also develop mucosal inflammation → backwash ileitis.
Only mucosa and submucosal layers of the colon are involvement, deep layer are not involved usually.
Isolated islands of regenerating mucosa bulge upward to create pseudopolyp.
There are a superficial mucosal ulcer but they are not serpentine as seen in CD.
Neutrophilic infiltration into crypts leads to the formation of crypt abscess.
In sever cases of UC, toxic damage to the muscular propria and neural plexus lead to complete shutdown of neuromuscular function →  colon progressively swells to create toxic megacolon.
There may be epithelial dysplasia with progression to frank carcinoma.