You are answering a USMLE-style medical question. Question: A 67-year-old woman with depression comes to the physician because of easy bruising and bleeding of her gums for the past 2 months. She has been living alone since the death of her husband 1 year ago. She appears thin and has temporal wasting bilaterally. Physical examination shows bruises on her lower legs, swollen gums, and petechiae on the hard palate. This patient's symptoms are most likely due to defective synthesis of a substance that is composed primarily of which of the following amino acids? Options: A) Glycine B) Proline C) Lysine D) Arginine Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.