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
Combination of sulfamethoxazole and trimethoprim is synergistic due to 
Select and explain. 
A. Enhanced entry into bacteria, B. Sequential blockade in folate metabolism, C. Inhibition of drug inactivation enzymes, D. Inhibition of drug efflux
B: Sequential blockade in folate metabolism
Answer: B: Sequential blockade in folate metabolism 
Explanation: None