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: Microbiology
Effective for common gram-negative anaerobes ? 
Select and explain. 
A. Aztreonam, B. Doxycycline, C. Vancomycin, D. Tobramycin
A: Aztreonam
Answer: A: Aztreonam 
Explanation: Ans. is 'a' i.e., Aztreonam