<prompt> The roots and trunks enter the posterior triangle of the neck by passingBetween the anterior scalene and middle scalene musclesBetween the middle scalene and posterior scalene musclesBehind subclavius musclePosterior and inferior subclavian Artery  <response>: The roots and trunks enter the posterior triangle of the neck by passing between the anterior scalene and middle scalene and lie posterior superior to subclavian Artery. 