What are the candidates in the district whose incumbent is Gus Yatron?
CREATE TABLE "table1_1341604_39" (
  "district" text,
  "incumbent" text,
  "party" text,
  "first_elected" real,
  "result" text,
  "candidates" text
);
SELECT "candidates" FROM "table1_1341604_39" WHERE "incumbent"='Gus Yatron';