what are all the gtc winners for pole position no. 21 team modena
CREATE TABLE "calendar" (
  "round" real,
  "circuit" text,
  "date" text,
  "length" text,
  "pole_position" text,
  "gt3_winner" text,
  "gtc_winner" text
);
SELECT "gtc_winner" FROM "calendar" WHERE "pole_position"='No. 21 Team Modena';