user: Question: who is the constructor when the laps is less than 68, the grid is more than 20 and the driver is Thierry Boutsen?
Columns: ['Driver', 'Constructor', 'Laps', 'Time/Retired', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Gerhard Berger', 'Benetton - BMW', 68.0, '1:33:18.700', 4.0]
SQL:

assistant: SELECT "Constructor" FROM "Table" WHERE "Laps" < 68.0 AND "Grid" > 20.0 AND "Driver" = 'Thierry Boutsen';