<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 50-year-old woman presents to the clinic with joint pain that has persisted for the last 2 months. She reports having intermittently swollen, painful hands bilaterally. She adds that when she wakes up in the morning, her hands are stiff and do not loosen up until an hour later. The pain tends to improve with movement. Physical examination is significant for warm, swollen, tender proximal interphalangeal joints, metacarpophalangeal joints, and wrists bilaterally. Laboratory results are positive for rheumatoid factor 4-fold greater than the upper limit of normal ULN and anti-cyclic citrullinated peptide anti-CCP antibodies 3-fold greater than ULN. CRP and ESR are elevated. Plain X-rays of the hand joints show periarticular osteopenia and bony erosions. She was started on the first-line drug for her condition which inhibits dihydrofolate reductase. Which medication was this patient started on?? A: 5-fluorouracil, B: Leflunomide, C: Methotrexate, D: Hydroxyurea, E: Allopurinol,  <response>: This is a patient with a 2-month history of joint pain, morning stiffness, and physical exam findings consistent with rheumatoid arthritis. Key laboratory findings include elevated rheumatoid factor, anti-CCP antibodies, CRP, and ESR. X-ray findings of periarticular osteopenia and erosions also support the diagnosis of rheumatoid arthritis. The question asks about the first-line medication this patient was started on, which inhibits dihydrofolate reductase. Methotrexate is a first-line disease-modifying antirheumatic drug DMARD for rheumatoid arthritis that works by inhibiting dihydrofolate reductase. The other answer choices are not first-line options for rheumatoid arthritis treatment.C: Methotrexate 