user: Question: The U.S. airdate of 4 April 2008 had a production code of what?
Columns: ['No. in season', 'No. in series', 'Title', 'Canadian airdate', 'US airdate', 'Production code']
Types: ['real', 'real', 'text', 'text', 'text', 'real']
Sample row: [1.0, 120.0, '"Standing in the Dark" Part One', '14 January 2008', '5 October 2007', 701.0]
SQL:

assistant: SELECT "Production code" FROM "Table" WHERE "US airdate" = '4 April 2008';