What are the most wins in 1971 in 250cc class?
CREATE TABLE "grand_prix_motorcycle_racing_results" (
  "year" real,
  "class" text,
  "team" text,
  "points" real,
  "rank" text,
  "wins" real
);
SELECT MAX("wins") FROM "grand_prix_motorcycle_racing_results" WHERE "class"='250cc' AND "year"=1971;