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: Unknown
Young lady presents with acute abdominal pain and history of 1 1/2 months amenorrhoea on USG examination there is a collection of fluid in the pouch of Douglas and empty uterine cavity. Diagnosis is 
Select and explain. 
A. Ectopic pregnancy, B. Pelvic hematocele, C. Threatened abortion, D. Twisted ovarian cyst
A: Ectopic pregnancy
Answer: A: Ectopic pregnancy 
Explanation: Ans-A ectopic pregnancy (Ref Dutta, 6/e, p 186 (5/e, p. 198, 4/e, pl98)).History of amenorrhoea and absence of gestational sac and collection of fluid in the pouch of Douglas leaves no doubt about the diagnosis of ectopic pregnancy.