Question: When did the county of Virginia whose FIPS 6-4 (US counties) is 51015, has a population of 73912?
Choices:
1991
2001-12-19
1955-09-24
1685
2013-07-01
2015-09-30
2001-07-18
1940-04-01
1771-01-01
1922-12-01