A 9-year-old child has suddenly collapsed. After confirming that the scene is safe, a single rescuer determines that the child is in cardiac arrest, shouts for nearby help, and activates the emergency response system by using his mobile device. He immediately begins performing high-quality CPR. Two additional rescuers immediately arrive to assist in the resuscitation attempt. Two rescuers begin high-quality CPR while the third rescuer leaves to get the AED. What action supports 2-rescuer CPR