You are answering a USMLE-style medical question. Question: A 28-year-old woman, gravida 2, para 1, at 40 weeks of gestation is admitted to the hospital in active labor. The patient has attended many prenatal appointments and followed her physician's advice about screening for diseases, laboratory testing, diet, and exercise. Her pregnancy has been uncomplicated. She has no history of a serious illness. Her first child was delivered via normal vaginal delivery. Her vital signs are within normal limits. Cervical examination shows 100% effacement and 10 cm dilation. A cardiotocograph is shown. Which of the following is the most appropriate initial step in management? Options: A) Amnioinfusion B) Induced vaginal delivery C) Reassurance D) Repositioning Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.