The correct answer is B) turn the patient's body to the side, sweep out the mouth and resume mouth-to-mouth ventilation. This is the correct answer because it is the first and most important action the rescuer must take if the patient vomits during mouth-to-mouth resuscitation. Turning the patient's body to the side allows the vomit to drain out of the mouth, preventing it from being inhaled and potentially causing further complications. Sweeping out the mouth removes any remaining vomit or obstructions, allowing the rescuer to resume effective mouth-to-mouth ventilation. The other options are incorrect because: A) switching to mouth-to-nose ventilation does not address the immediate issue of clearing the airway; C) ignoring the vomiting and continuing mouth-to-mouth ventilation could lead to aspiration of the vomit; and D) pausing until the patient appears quiet again delays the necessary action of clearing the airway.