CREATE TABLE table_49817 ("Name" CLOB, "Built" CLOB, "Listed" CLOB, "Location" CLOB, "County" CLOB)

When was the oakachoy covered bridge listed?
SELECT "Listed" FROM table_49817 WHERE "Name" = 'oakachoy covered bridge'
SELECT "Listed" FROM "table_49817" WHERE "Name" = 'oakachoy covered bridge'