You are answering a USMLE-style medical question. Question: The patient is given prophylactic labetalol and magnesium sulfate. Examination shows absent deep tendon reflexes bilaterally. Which of the following is the most appropriate next step in the management of this patient? Options: A) Stop magnesium sulfate and give calcium gluconate B) Stop labetalol C) Stop magnesium sulfate and give lorazepam D) Perform nerve conduction studies Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.