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
Alkylating drugs attach alkyl group to _________ position of guanine 
Select and explain. 
A. N3, B. N5, C. N7, D. N9
C: N7
Answer: C: N7 
Explanation: Alkylating drugs attach alkyl group to N7 of Guanine and results in mispairing of nitrogenous bases.