<prompt> At hilum of lung, what enters -PrimaryPrincipal bronchusSecondary bronchusTertiary bronchusBronchiole  <response>: Ans. is a i.e., PrimaryPrincipal bronchus o The root hilum of lung is made up of following structuresPrincipal bronchus on the left side, and eparterial and hvparterial bronchi on the right side.One pulmonary artery.Two pulmonary veins, superior and inferior.Bronchial arteries, one on the right side and two on the left side.Bronchial veins.Anterior and posterior pulmonary plexuses of nerves.Lymphatics of the lung.Bronchopulmonary lymph nodes.Areolar tissue. 