You have arrived on the scene at a high school football field where a 17-year-old male is lying on the ground. he is unresponsive and cyanotic, and he is making obvious respiratory effort without moving adequate amounts of air. which of the following should be done first? a. apply high-concentration oxygen by nonrebreather mask. b. insert a nasopharyngeal or oropharyngeal airway. c. assist ventilations with a bag-valve-mask device and supplemental oxygen. d. open the patient's airway using a manual maneuver.