What is the round for the opponent CSKA Sofia in Venue A?
CREATE TABLE "uefa_cup_winner_s_cup" (
  "date" text,
  "round" text,
  "opponent" text,
  "venue" text,
  "result" text,
  "attendance" real
);
SELECT "round" FROM "uefa_cup_winner_s_cup" WHERE "opponent"='cska sofia' AND "venue"='a';