user: Question: Who was the co-driver in the DNF position in the GT1 class?
Columns: ['Year', 'Team', 'Co-Drivers', 'Class', 'Pos.', 'Class Pos.']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1984.0, 'Martini Racing', 'Paolo Barilla Hans Heyer', 'C1', 'DNF', 'DNF']
SQL:

assistant: SELECT "Co-Drivers" FROM "Table" WHERE "Pos." = 'DNF' AND "Class" = 'GT1';