<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 68-year-old man undergoes successful mechanical prosthetic aortic valve replacement for severe aortic valve stenosis. After the procedure, he is started on an oral medication and instructed that he should take for the rest of his life and that he should avoid consuming large amounts of dark-green, leafy vegetables. Which of the following laboratory parameters should be regularly monitored to guide dosing of this drug?? A: Anti-factor Xa activity, B: Thrombin time, C: Activated partial thromboplastin time, D: D-dimer, E: Prothrombin timen,  <response>: This is a question about anticoagulation therapy after aortic valve replacement surgery. The patient has undergone a mechanical prosthetic aortic valve replacement, which requires lifelong anticoagulation to prevent valve thrombosis. The medication he is started on is likely warfarin, a vitamin K antagonist. Warfarin works by inhibiting vitamin K-dependent clotting factors II, VII, IX, and X. The question asks which laboratory parameter should be monitored to guide warfarin dosing. Choice A, anti-factor Xa activity, is used to monitor direct factor Xa inhibitors like apixaban but not warfarin. Choice B, thrombin time, is overly sensitive to warfarin and not used for monitoring. Choice C, activated partial thromboplastin time aPTT, can be prolonged with warfarin but is not the ideal test. Choice D, D-dimer, indicates clot formation but does not reflect warfarin effect. Choice E, prothrombin time PTinternational normalized ratio INR, is the correct answer. The PTINR specifically measures factors II, VII, and X, which are inhibited by warfarin. Regular PTINR monitoring is required to maintain the therapeutic range for warfarin dosing.E: Prothrombin time 