Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Title | Length | Writer | Director | Airdate |
| --- | --- | --- | --- | --- |
| "Episode 1" | 60 minutes | Sarah Phelps | Coky Giedroyc | 18 December 2007 |
| "Episode 2" | 30 minutes | Sarah Phelps | Coky Giedroyc | 19 December 2007 |
| "Episode 3" | 30 minutes | Sarah Phelps | Coky Giedroyc | 20 December 2007 |
| "Episode 4" | 30 minutes | Sarah Phelps | Coky Giedroyc | 21 December 2007 |
| "Episode 5" | 30 minutes | Sarah Phelps | Coky Giedroyc | 22 December 2007 |
Question:
The length of 30 minutes aired on what date?
Answer:
19 December 2007, 20 December 2007, 21 December 2007, 22 December 2007