CREATE TABLE table_204_834 (id DECIMAL, "rank" DECIMAL, "name" TEXT, "nationality" TEXT, "time" TEXT)

who was the last finisher from the us ?
SELECT "name" FROM table_204_834 WHERE "nationality" = 'united states' ORDER BY "time" DESC LIMIT 1
SELECT "name" FROM "table_204_834" WHERE "nationality" = 'united states' ORDER BY "time" DESC NULLS LAST LIMIT 1