What is every value for average on previous season if the competition is league two?
CREATE TABLE "average_crowd_sizes" (
  "season" text,
  "ave_attendance" real,
  "ave_on_prev_season" text,
  "competition" text,
  "occupier" text
);
SELECT "ave_on_prev_season" FROM "average_crowd_sizes" WHERE "competition"='League Two';