a) The correct tube for swalloing is the esophagus, from the digestive system. However, it stands side by side with another tube from the respiratory system, and if the food gets into the respiratory system it would get into the wrong tube and the person will choke until the food is expelled. The name of this wrong tube is trachea.
b) There is a structure made of a flap tissue that covers the trachea when you are swallowing, so the food won't go down there. This structure is called epiglottis.
