You are answering a USMLE-style medical question. Question: A 30-year-old woman comes to the physician because of increasing weakness in both legs for 7 days. She also reports a tingling sensation in her legs that is exacerbated by taking a hot shower. She is sexually active with one male partner and does not use condoms. Her temperature is 37.8°C (100.1°F). Physical examination shows decreased muscle strength and clonus in both lower extremities. Patellar reflex is 4+ bilaterally and plantar reflex shows an extensor response on both sides. Abdominal reflex is absent. An MRI of the brain is shown. Which of the following findings is most likely to further support the diagnosis in this patient? Options: A) Positive antibody response to cardiolipin-cholesterol-lecithin antigen in the serum B) Oligodendrocytes that stain positive for polyomavirus proteins on brain biopsy C) Presence of immunoglobulin bands on cerebrospinal fluid immunofixation D) Identification of gram-positive cocci in groups on blood culture Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.