user: Question: What is the region 1 where region 4 is TBA is The Complete Eighth Series?
Columns: ['Complete Series', 'Region 1', 'Region 2', 'Region 4', 'DVD Extras and Bonus Features', 'Number Of Discs']
Types: ['text', 'text', 'text', 'text', 'text', 'real']
Sample row: ['The Complete Second Series', 'TBA', '4 September 2007', '12 November 2008', 'Unseen Footage', 2.0]
SQL:

assistant: SELECT "Region 1" FROM "Table" WHERE "Region 4" = 'TBA' AND "Complete Series" = 'The Complete Eighth Series';