user: Question: When was Shannon Long the Centerfold model?
Columns: ['Date', 'Cover model', 'Centerfold model', 'Interview subject', '20 Questions']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['1-88', 'none', 'Kimberley Conrad', 'Arnold Schwarzenegger', 'Susan Dey']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Centerfold model" = 'Shannon Long';