Which structure at the tracheal bifurcation triggers violent coughing when food touches it?

1. The trachea branches into the right and left primary bronchi at the carina. 2. The carina is a raised structure carrying specialised nervous tissue. 3. Contact with a foreign body such as food induces violent coughing, so the third option is correct. 4. The hilum is where vessels and bronchi enter the lung and has no such cough reflex tissue, ruling out the first option. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 22 "The Respiratory System", section 22.1 Organs and Structures of the Respiratory System_