user: Question: What was the production code of the episode ranked 28?
Columns: ['No.', '#', 'Title', 'Directed by', 'Written by', 'U.S. viewers (million)', 'Rank (week)', 'Original air date', 'Production code']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [48.0, 1.0, '"Sacrifice"', 'David Mamet', 'Frank Military', '9.71 (repeat: 3.9 on February 1 , 2009 at 9pm)', '29', 'September28,2008', '4ALF01']
SQL:

assistant: SELECT "Production code" FROM "Table" WHERE "Rank (week)" = '28';