Final answer:
Headrests should be adjusted to make contact with the back of the head to prevent neck injuries such as whiplash from rear-end collisions, corresponding to option C.
Step-by-step explanation:
Headrests in vehicles are designed to prevent neck injuries if the car is hit from behind. This is because the anterior longitudinal ligament, which runs down the front of the vertebral column, can be stretched or torn during such accidents. This type of injury is known as whiplash, which was much more common before the mandatory installation of headrests. The proper adjustment of headrests ensures that in the event of a rear collision, the head and neck are supported, reducing the likelihood of extreme backward bending that could result in injury.
Other safety features in vehicles, such as airbags and crumple zones, contribute to passenger protection by extending the time of impact and reducing the force exerted on occupants during a collision. The principle of impulse suggests that increasing the time over which a force acts reduces the force. This is why padded dashboards, airbags, and crumple zones are critical, as they help to absorb and spread out force, making impacts less severe.
In conclusion, headrests should be properly adjusted so that the head restraint contacts the back of the head, preventing neck injuries like whiplash in the event of a rear-end collision, which aligns with option C.