user: Question: What is the average Channel 4 weekly rank for less than 2.19 million viewers on December 7, 2007?
Columns: ['Episode #', 'Title', 'Airdate', 'Viewers (millions)', 'Channel 4 weekly rank a']
Types: ['real', 'text', 'text', 'real', 'real']
Sample row: [24.0, '"How Betty Got Her Grieve Back', 'October 5, 2007', 2.82, 1.0]
SQL:

assistant: SELECT AVG("Channel 4 weekly rank a") FROM "Table" WHERE "Viewers (millions)" < 2.19 AND "Airdate" = 'December 7, 2007';