Table: regional_airliners
Columns: model
seats
period
built
country

Question: In what time period were 578 built?
SQL: SELECT "period" FROM regional_airliners WHERE "built" = '578'

Question: In what time period was the Cessna 208 built?
SQL: SELECT "period" FROM regional_airliners WHERE "model" = 'cessna 208'

Question: In what time period were 354 built?
SQL: SELECT "period" FROM regional_airliners WHERE "built" = '354'