A nurse is reinforcing teaching with new parents about car seat safety. Which of the following instructions should the nurse include?

Choice A reason: Shoulder harnesses at shoulder level secure the infant, distributing crash forces evenly. Scientifically, this aligns with safety standards, preventing spinal injury by stabilizing the torso, a critical car seat feature per biomechanical crash studies for optimal protection.Choice B reason: A cushion under the head risks airway obstruction or spinal misalignment in crashes. Scientifically, added padding alters manufacturer design, increasing injury risk, as car seats are engineered for direct fit without extras per safety regulations.Choice C reason: A 90-degree angle is upright, risking airway collapse in newborns with weak necks. Scientifically, a 30-45-degree recline supports breathing and spinal alignment, making this unsafe per pediatric and crash safety evidence.Choice D reason: Airbags in the front seat can fatally injure infants in rear-facing seats via rapid inflation. Scientifically, back-seat placement avoids this, as airbag force exceeds infant tolerance, contradicting safety mandates for car seat positioning.