Which structure enters into the lungs?

ANSWER: (B) Left principle bronchusREF: Gray's anatomy 40th ed ch: 57The right main bronchus gives rise to its first branch, the superior lobar bronchus, then enters the right lung opposite the fifth thoracic vertebra.The left principal bronchus, which is narrower and less vertical than the right, is 5 cm long. Passing to the left inferior to the aortic arch, it crosses anterior to the oesophagus, thoracic duct and descending aorta; the left pulmonary artery is at first anterior and then superior to it. Itenters the hilum of the Is ft lung at the level of the sixth thoracic vertebra and divides into a superior and an inferior lobar bronchus.