You are answering a USMLE-style medical question. Question: A 55-year-old construction worker is struck by a high-voltage power line while on duty. According to bystanders, the cable struck him on his right arm, after which the man slumped to the ground with his arms and legs shaking. In the emergency department, the man is alert but in severe pain localizing bilaterally in the flanks as well as in his right arm where contact with the power line occurred. A 6 cm burn is present on the right arm. His vitals are within normal limits except for mild tachypnea at 21/min. Which of the following diagnostic tests should be conducted first to evaluate this patient? Options: A) FAST ultrasound assessment B) Urinalysis C) X-ray of the arm and shoulder D) EEG Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.