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
Which drug is not effective against H.pylori- 
Select and explain. 
A. Colloidal Bismuth, B. Metronidazole, C. Amoxicillin, D. Erythromycin
D: Erythromycin
Answer: D: Erythromycin 
Explanation: None