Final answer:
Helmets should be replaced every few years due to wear and tear from use which can degrade their protective capabilities despite not always being visible. The materials inside the helmet can deteriorate, compromising safety.
Step-by-step explanation:
It is strongly recommended that your helmet be replaced every few years due to c) Wear and tear from use. Helmets are made of materials that can deteriorate over time, which may not be visible to the eye. Exposure to various external factors such as UV radiation, moisture, and temperature changes can degrade a helmet's protective capabilities. The foam and other materials inside the helmet can also compress or become damaged with regular use, reducing the level of protection in the event of an impact. To ensure maximum safety and prevent nervous system injuries, which could cause lifelong disability, it is crucial to replace helmets periodically.