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: Pharmacology
Tetracyclines are not useful for : 
Select and explain. 
A. Trichomonas, B. Chlamydia, C. Syphilis, D. Rickettsia
A: Trichomonas
Answer: A: Trichomonas 
Explanation: None