Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the average Channel 4 weekly rank for less than 2.19 million viewers on December 7, 2007?

### Inputs:
table_name: table, columns: ['Episode #', 'Title', 'Airdate', 'Viewers (millions)', 'Channel 4 weekly rank a']

### Response:
SELECT AVG Channel 4 weekly rank a FROM table WHERE Viewers (millions) < 2.19 AND Airdate = december 7, 2007