user: Question: What's the period of a Rock album released in 1973?
Columns: ['Artist', 'Country of origin', 'Period active', 'Release-year of first charted record', 'Genre', 'Claimed sales']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Eagles', 'United States', '1971–present', 1972.0, 'Soft rock / Country rock', '150 million']
SQL:

assistant: SELECT "Period active" FROM "Table" WHERE "Release-year of first charted record" = 1973.0 AND "Genre" = 'Rock';