The patient is a newborn delivered vaginally during the 41st week of gestation at a regional medical center after prolonged and difficult labor. The newborn is vigorous and has normal vital signs. At rest the newborn's right arm is held in an adducted and medially rotated position, the forearm is held in an extended and pronated position, and the wrist is slightly flexed. Physical examination reveals a loss of arm abduction and lateral rotation, loss of supination, and weakness in forearm flexion and wrist extension. There is also loss of sensation along the right upper limb's lateral arm, lateral forearm, and thumb. Where is the most likely location of the injury?
1) right upper trunk of the brachial plexus
2) right posterior cord of the brachial plexus
3) roots of right spinal nerve T1
4) right lower trunk of the brachial plexus
5) right lateral cord of the brachial plexus