user: Question: Which production code had original air dated February20,2011
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (million)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [148.0, 1.0, '" And Then There Were Fewer "', 'Dominic Polcino', 'Cherry Chevapravatdumrong', 'September26,2010', '8ACX01/8ACX02', '9.41']
SQL:

assistant: SELECT "Production code" FROM "Table" WHERE "Original air date" = 'February20,2011';