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
Which of the following is not effective against anaerobes ? 
Select and explain. 
A. Gentamycin, B. Cefotetan, C. Imipenem, D. Clindamycin
A: Gentamycin
Answer: A: Gentamycin 
Explanation: Ans. is 'a' i.e., Gentamycin