<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 3629-g 8-lb newborn is examined shortly after spontaneous vaginal delivery. She was delivered at 40 weeks gestation and pregnancy was uncomplicated. Her mother is concerned because she is not moving her left arm as much as her right arm. Physical examination shows her left arm to be adducted and internally rotated, with the forearm extended and pronated, and the wrist flexed. The Moro reflex is present on the right side but absent on the left side. Which of the following brachial plexus structures is most likely injured in this infant?? A: Upper trunk, B: Long thoracic nerve, C: Lower trunk, D: Axillary nerve, E: Posterior cord,  <response>: This is a clinical vignette describing a newborn with asymmetric arm movements, suggesting a brachial plexus injury. The key findings are:- Newborn girl delivered vaginally at full term - Left arm held in adduction, internal rotation, forearm pronation, wrist flexion- Absent Moro reflex on left side- Concern for brachial plexus injuryBased on the presentation, this is most consistent with an Erbs palsy, which involves injury to the upper trunk C5-C6 of the brachial plexus. The pattern of arm positioning and absent Moro reflex localizes the injury to the upper trunk.A: Upper trunk 