What is the average number of House of Representatives seats had an abbreviation of d66?
CREATE TABLE "parliamentary_parties" (
  "abbr" text,
  "political_leader" text,
  "international_affiliation" text,
  "votes_2012" text,
  "house_of_rep_seats" real,
  "senate_seats" real,
  "european_parliament_seats" real
);
SELECT AVG("house_of_rep_seats") FROM "parliamentary_parties" WHERE "abbr"='d66';