What prevents food or liquids from getting in the lungs?

Epiglottis

Explanation:

Trachea is called windpipe which is responsible for passage of air into the lungs and the esophagus is a food pipe that is responsible for the passage of food into the stomach.  

When we swallow liquid and food the tracheal opening is closed by a leaf shapes flap called epiglottis. So this epiglottis prevents food and liquid from getting into the lungs by covering the windpipe opening. This is the reason we do not take oxygen and swallow food simultaneously.

that is correct.

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