What is the highest Version, when Release Date is "2011-04-01"?
CREATE TABLE "zune_hd_games" (
  "title" text,
  "developer" text,
  "genre" text,
  "release_date" text,
  "version" real
);
SELECT MAX("version") FROM "zune_hd_games" WHERE "release_date"='2011-04-01';