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
All of the following are effective in giardiasis except 
Select and explain. 
A. Co-trimoxazole, B. Furazolidine, C. Metronidazole, D. Tinidazole
A: Co-trimoxazole
Answer: A: Co-trimoxazole 
Explanation: None