You are answering a USMLE-style medical question. Question: A previously healthy 18-year-old army recruit is brought to a military treatment facility because of a 3-week history of right foot pain. He recently started basic infantry training and has been running several kilometers daily. Initially, the pain only occurred while running, but now it is also present at rest. The pain is located diffusely over the right forefoot. Vital signs are within normal range. Examination shows mild swelling over the distal right forefoot. Pressing the metatarsal of the third right toe results in pain. He walks with an antalgic gait. The remainder of the examination shows no abnormalities. An x-ray of the right foot shows a slight loss of cortical density and callus formation at the third metatarsal shaft. Which of the following is the most appropriate next step in management? Options: A) Rest and acetaminophen B) Ultrasonography C) Technetium bone scan D) Internal fixation Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.