user: Question: How many millions of U.S. viewers watched the episode directed by Allison Liddi-Brown? 
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'U.S. viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: [143.0, 1.0, '"Resurrection" (Part 2)', 'Joe Chappelle', "Barry O'Brien", 'September22,2008', '17.23']
SQL:

assistant: SELECT "U.S. viewers (millions)" FROM "Table" WHERE "Directed by" = 'Allison Liddi-Brown';