You are answering a USMLE-style medical question. Question: A 64-year-old male presents to his primary care physician with a complaint of bilateral knee pain that has been present for the past several years but has worsened recently. He reports pain with climbing stairs and with extended walks of greater than 100 yards. The pain worsens with activity throughout the day and is alleviated by periods of rest. He states that he has minimal morning stiffness, lasting approximately 5-10 minutes after waking up most days. Physical examination reveals tenderness to palpation of the bony structures on the medial aspect of the bilateral knees as well as crepitus and a decreased range of motion, limited at the extremes of flexion and extension. Both knee joints are cool to touch and exhibit bony enlargement upon palpation of the medial joint line. Which of the following studies would be indicated for further work-up of this patient's presenting condition? Options: A) Complete blood count (CBC) B) Erythrocyte sedimentation rate (ESR) C) MRI of the knee D) No further work-up needed Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.