The traffic cop asked the driver if he happened to have a flux capacitor.
Where this man was going, he didn't need roads.
The boy emerged and introduced himself as Marty McFly, and asked if she was "The Harriet Tubman". Harriet did not say a word. he also knew there was a bounty on her head. This boy looked like he was intending to collect.
The official line on Back to the Future's origin states that co-writer Bob Gale was visiting his native Missouri, found his father's high school yearbook, and wondered if he'd have befriended him as a teen.