user: Question: What period was there a 22.7 NC?
Columns: ['Period', 'Live births per year', 'Deaths per year', 'Natural change per year', 'CBR*', 'CDR*', 'NC*', 'TFR*', 'IMR*', 'Life expectancy total', 'Life expectancy males', 'Life expectancy females']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'real', 'text', 'text', 'text']
Sample row: ['1950-1955', '10 000', '3 000', '7 000', '48.0', '14.9', '33.1', '6.56', 89.0, '56.0', '54.4', '57.7']
SQL:

assistant: SELECT "Period" FROM "Table" WHERE "NC*" = '22.7';