Final answer:
The appropriate size nasopharyngeal tube is selected based on the patient's age.
Step-by-step explanation:
The appropriate size nasopharyngeal tube is selected based on a patient's age, not the patient's weight, height, or gender. The age of the patient determines the size of the nasopharyngeal tube that should be used. This is because the size and anatomy of the nasopharynx can vary with age. For example, a larger size tube may be required for an adult compared to a child.