What is the Cause of death of the Officer with a Date of death of 1956-09-07?
CREATE TABLE "officers" (
  "rank" text,
  "badge_serial_number" text,
  "tenure" text,
  "date_of_death" text,
  "cause_of_death" text
);
SELECT "cause_of_death" FROM "officers" WHERE "date_of_death"='1956-09-07';