user: Question: Where was the landing site when the duration on the lunar surface was 21:31?
Columns: ['Mission name', 'Lunar lander', 'Lunar landing date', 'Lunar blastoff date', 'Lunar landing site', 'Duration on lunar surface', 'Crew', 'Number of s EVA', 'Total EVA Time (HH:MM)']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['Apollo 11', 'Eagle', '20 July 1969', '21 July 1969', 'Sea of Tranquility', '21:31', 'Neil Armstrong , Edwin "Buzz" Aldrin', 1.0, '2:31']
SQL:

assistant: SELECT "Lunar landing site" FROM "Table" WHERE "Duration on lunar surface" = '21:31';