When a child is old enough to ride in the front seat of a car, what is the proper way for them to be buckled in?

Answer: D — booster seat with a shoulder strap

When a child is old enough to ride in the front seat of a car, they should be properly buckled in with a booster seat that has a shoulder strap. This option provides the necessary height and support for the child to safely use the adult seat belt and shoulder strap. Option A is incorrect because a car seat with a shoulder strap is typically used for younger children and is not designed for use in the front seat. Option B is incorrect because a booster seat with just a lap belt does not provide adequate upper body support for the child. Option C is incorrect because a seat belt with just a shoulder strap is not suitable for a child in the front seat without a booster seat. Therefore, the most appropriate and safe option is D.