When the nurse is determining the appropriate size of an oropharyngeal airway to insert, what part of a client's body should she measure?

Correct! When sizing an oropharyngeal airway, the nurse should measure from the corner of the client's mouth to the tragus of the ear. This measurement ensures that the airway is the appropriate length to reach the pharynx without being too long or too short. Choices B, C, and D are incorrect as they do not provide the correct anatomical landmarks for determining the size of an oropharyngeal airway. Measuring from the corner of the mouth to the tragus of the ear is a standard method to ensure proper airway size and prevent complications during airway management.