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: Medicine
[{'content': 'All of the following are effective in giardiasis except \nSelect and explain. \nA. Co-trimoxazole, B. Furazolidine, C. Metronidazole, D. Tinidazole', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]