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: Surgery
A 12 month old male child suddenly draws up his legs and screams with pain. This is repeated periodically throughout the night interspersed with periods of quiet sleep. When seen after 12 hours the child looks pale, has just vomited andpassed thin blood-stained stool; there is a mass around umbilicus. What is the most likely diagnosis 
Select and explain. 
A. Appendicitis, B. Intussusception, C. Gastro-enteritis, D. Roundworm obstruction
B: Intussusception
Answer: B: Intussusception 
Explanation: Ans. is 'b' i.e., Intussusception