Final answer:
The staff nurse should suction the oropharyngeal cavity prior to suctioning the endotracheal tube to ensure proper suctioning and prevent the risk of aspirating secretions or debris into the lower airway.
Step-by-step explanation:
The correct statement that indicates an understanding of the teaching about endotracheal suctioning is option C: 'I will suction the oropharyngeal cavity prior to suctioning the endotracheal tube.' This statement shows the understanding that it is important to clear the upper airway before suctioning the endotracheal tube to prevent the risk of aspirating secretions or debris into the lower airway. Suctioning the oropharyngeal cavity first helps remove any potential obstructions or secretions that may hinder proper suctioning of the endotracheal tube.