This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parasitology, Subject name: Microbiology
A patient presents with lower gastrointestinal bleed. Sigmoidoscopy shows ulcer in the sigmoid. Biopsy from this area shows flask-shaped ulcers. Which of the following is the most appropriate treatment? 
Select and explain. 
A. Intravenous ceftriaxone, B. Intravenous metronidazole, C. Intravenous steroids and sulphasalazine, D. Hydrocortisone enemas
B: Intravenous metronidazole
Answer: B: Intravenous metronidazole 
Explanation: Ans. is 'b' i.e., Intravenous metronidazole(Ref: Harrison, 18th/e, p. 1686; 17th/e, p. 1278)* Flask-shaped ulcer in a patient of GI bleed suggests amoebiasis (amoebic dysentery).* Metronidazole or Tinidazole are the DOCs.