What Piece of Information Would You Provide to a Group

What piece of information would you provide to a group of young teenage drivers to decrease their chance of suffering a "whiplash" type injury if involved in a motor vehicle collision?

A) Ensure that the head rest is properly positioned.
B) Position the car's seats in a full upright position.
C) Make sure the car has side door air bags.
D) Properly wear seat belts with a headrest in the down position.