user: Question: What is the airing date for a Modern drama with more than 21 episodes?
Columns: ['Airing date', 'English title (Chinese title)', 'Number of episodes', 'Genre', 'Official website']
Types: ['text', 'text', 'real', 'text', 'text']
Sample row: ['7 Dec 2005- 4 Jan 2006', 'When Rules Turn Loose 識法代言人', 21.0, 'Modern drama', 'Official website']
SQL:

assistant: SELECT "Airing date" FROM "Table" WHERE "Genre" = 'Modern drama' AND "Number of episodes" > 21.0;