The correct answer is C) Re-tip the head and try again. If no air is getting into the victim's lungs when you are blowing into their mouth, it likely indicates an obstruction in the airway that is preventing the air from reaching the lungs. The proper response is to re-tip the victim's head to re-establish an open airway, and then try ventilating them again. This maneuver helps ensure the head is properly tilted back to lift the tongue away from the back of the throat, which is a common cause of airway obstruction. The other options are incorrect because they do not address the primary issue of the obstructed airway. Raising the victim's head higher (A), blowing harder (B), or pressing on the lungs (D) will not resolve the underlying airway obstruction and may even worsen the situation. Properly re-tipping the head is the appropriate first step to restore an open airway and allow effective ventilation.