Which category earlier than 2006 has Bart Brentjens as rider 2?
CREATE TABLE "winners_from_2004" (
  "date" real,
  "category" text,
  "team" text,
  "rider_1" text,
  "rider_2" text
);
SELECT "category" FROM "winners_from_2004" WHERE "date"<2006 AND "rider_2"='bart brentjens';