CREATE TABLE table_45507 ("Pinnacle height" TEXT, "Year" FLOAT, "Structure type" TEXT, "Main use" TEXT, "Country" TEXT, "Town" TEXT)

What year was the structure in greensboro, north carolina considered tallest?
SELECT "Year" FROM table_45507 WHERE "Town" = 'greensboro, north carolina'
SELECT "Year" FROM "table_45507" WHERE "Town" = 'greensboro, north carolina'