Question: When did a capital of  Luxembourg (the one whose marriageable age is 18 years old) reach the population of 15,091 people ?
Choices:
2012-06-30
1821-01-01
1631-01-01
1813-01-01
1835-01-01
1978-05-01
1541
1861-01-01
2002-11-20
2011-08-01