In what county is the entry that has a Construction Completed date of 07/19/2000 and a Listed date of 09/21/1984 located?
CREATE TABLE "superfund_sites" (
  "cerclis_id" text,
  "name" text,
  "county" text,
  "proposed" text,
  "listed" text,
  "construction_completed" text,
  "partially_deleted" text,
  "deleted" text
);
SELECT "county" FROM "superfund_sites" WHERE "listed"='09/21/1984' AND "construction_completed"='07/19/2000';