user: Question: What Chassis ranked 18th?
Columns: ['Year', 'Entrant', 'Class', 'Chassis', 'Engine', 'Tyres', 'Rank', 'Points']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text', 'real']
Sample row: [1999.0, 'Audi Sport Team Joest', 'LMP', 'Audi R8R', 'Audi 3.6L Turbo V8', 'M', '52nd', 20.0]
SQL:

assistant: SELECT "Chassis" FROM "Table" WHERE "Rank" = '18th';