Rivers must dim their high beam headlights when within _____ of an oncoming vehicle

Answer: D — 500 feet

Rivers must dim their high beam headlights when within 500 feet of an oncoming vehicle because high beams can be blinding to drivers in the oncoming lane, potentially causing accidents or creating dangerous situations on the road. This distance allows for better visibility for all drivers involved and helps prevent glare that can hinder the ability to see clearly. It is essential to follow this rule to promote safety and courtesy while driving.