When operated on a highway at night, such slow-moving vehicles as animal-drawn carts, farm tractors, and road machinery must have __________ that are visible for 1,000 feet.

1. two red lights on the front and two white lights on the rear
2. one white light on the front and two red lights on the rear
3. two white lights on the front and two white lights on the rear
4. two red lights on the front and two red lights on the rear