The nasal endotracheal tube is not an appropriate intervention for an infant with choanal atresia because it cannot bypass the nasal blockage, unlike oral airway interventions.
The question 'Which is not an appropriate intervention for opening the airway in an infant with choanal atresia?' refers to emergency medical treatment procedures. Choanal atresia is a condition where the back of the nasal passage is blocked, typically by abnormal bony or soft tissue. For an infant with choanal atresia, the nasal passages would not be a reliable route for an airway.
Therefore, C. nasal endotracheal tube is not an appropriate intervention since it would not bypass the blockage in the nasal passages. The other listed options, A. McGovern nipple (which allows mouth breathing), B. oral endotracheal tube (which goes through the mouth), and D. oral guedel airway (a device to keep the oral airway open), are appropriate interventions provided they are sized and used correctly for an infant.