b. flap of cartilage that flips down to cover the entry to the trachea during swallowing
Explanation:
The function of the epiglottis is to prevent food and liquids from entering the windpipe (trachea) and the lungs. It is a flap of cartilage that stands upright when we breathe, allowing air to pass into the larynx and lungs. But while we are eating or drinking, it flips down over the opening of the trachea to prevent food and liquids from getting in there.
