CREATE TABLE table_29507 ("Period" CLOB, "Live births per year" CLOB, "Deaths per year" CLOB, "Natural change per year" CLOB, "CBR*" CLOB, "CDR*" CLOB, "NC*" CLOB, "TFR*" CLOB, "IMR*" FLOAT, "Life expectancy total" CLOB, "Life expectancy males" CLOB, "Life expectancy females" CLOB)

What period was there a 22.7 NC?
SELECT "Period" FROM table_29507 WHERE "NC*" = '22.7'
SELECT "Period" FROM "table_29507" WHERE "NC*" = '22.7'