Marcell Jansen with a transfer window of summer, and of transfer as type is from what nation?
CREATE TABLE "transfers_out" (
  "nat" text,
  "name" text,
  "type" text,
  "transfer_window" text,
  "transfer_fee" text
);
SELECT "nat" FROM "transfers_out" WHERE "transfer_window"='summer' AND "type"='transfer' AND "name"='marcell jansen';