user: Question: what is the engine when the tyre is D, the constructor is ERA anD the Driver is Bob Gerard?
Columns: ['Driver', 'Entrant', 'Constructor', 'Chassis', 'Engine', 'Tyre']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['José Froilán González', 'Scuderia Achille Varzi', 'Maserati', 'Maserati 4CLT-48', 'Maserati L4s', 'P']
SQL:

assistant: SELECT "Engine" FROM "Table" WHERE "Tyre" = 'D' AND "Constructor" = 'ERA' AND "Driver" = 'Bob Gerard';