What is the highest value for SF round for the country of England?
CREATE TABLE "2008_season" (
  "sf_round" real,
  "country" text,
  "location" text,
  "date" text,
  "driver" text,
  "race_1_pts" real,
  "race_2_pts" real,
  "race_total_pts" real
);
SELECT MAX("sf_round") FROM "2008_season" WHERE "country"='England';