What is the GP winner for the Race winners valentin giraud / nicolas musset, and a place genk?
CREATE TABLE "2013" (
  "date" text,
  "place" text,
  "race_winners" text,
  "gp_winner" text,
  "source" text
);
SELECT "gp_winner" FROM "2013" WHERE "race_winners"='valentin giraud / nicolas musset' AND "place"='genk';