This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anatomy
All are examples of competitive enzyme blockage except 
Select and explain. 
A. Cyclooxygenase by Aspirin, B. Thymidylate synthase by 5-FU, C. Coagulation by Dicumarol, D. DHFR by Methotrexate
A: Cyclooxygenase by Aspirin
Answer: A: Cyclooxygenase by Aspirin 
Explanation: Kinetics of enzyme inhibition Competitive inhibitionNon competitive inhibitionKm Increased No change V max No change Decreased Significance Drug action Toxicological (Refer: Harper's Illustrated Biochemistry, 26th edition, pg no: 67-68)