user: Question: What is the earliest year that had a co-driver of Roger Enever?
Columns: ['Year', 'Class', 'Tyres', 'Team', 'Co-Drivers', 'Pos.', 'Class Pos.']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1971.0, 'P 2.0', 'D', 'Camel Filters Team Huron', 'Roger Enever', 'DNF', 'DNF']
SQL:

assistant: SELECT MIN("Year") FROM "Table" WHERE "Co-Drivers" = 'Roger Enever';