user: Question: Who wrote the episode that aired on April 17, 2011? 
Columns: ['No. in season', 'No. in series', 'Title', 'Directed by', 'Written by', 'Original air date', 'U.S. viewers (million)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 69.0, '"Line of Departure"', 'John T. Kretchmer', 'Debra Fordham', 'March 6, 2011', '4.2']
SQL:

assistant: SELECT "Written by" FROM "Table" WHERE "Original air date" = 'April 17, 2011';