user: Question: Who directed the episode that was viewed by 2.50 million people in the U.S.?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [89.0, 1.0, '" 4 Years, 6 Months, 2 Days "', 'Greg Prange', 'Mark Schwahn', 'January8,2008', '3T6801', '3.36']
SQL:

assistant: SELECT "Directed by" FROM "Table" WHERE "U.S. viewers (millions)" = '2.50';