Final answer:
The correct statement is that cough receptors are located at the carina, which is where the trachea branches into the two primary bronchi.
Step-by-step explanation:
The true statement regarding the airways is A. Cough receptors lie at the carina. The carina is indeed a raised structure that contains specialized nervous tissue, which can induce violent coughing if a foreign body, such as food, is accidentally inhaled. The carina is not located in the right main stem bronchus; rather, it is found where the trachea branches into the right and left primary bronchi. There are only two primary bronchi, not three, and each primary bronchus branches into multiple secondary or lobar bronchi. Specifically, there are two secondary bronchi in the left lung and three in the right, totaling five.