Why is it important to replace a motorcycle helmet that has been subjected to a severe impact, even if no exterior shell cracks are visible?

1. The internal expanded polystyrene (EPS) foam liner crushes to absorb energy during impact and does not recover, losing all future shock absorption capability
2. The outer shell always cracks visibly when the helmet has been compromised
3. A helmet regains its protection once the liner has been allowed to rest for a few days
4. Replacement is needed only if the chinstrap or its buckle was damaged