What was the cause of death in the marriage that lasted 28 years? 
CREATE TABLE "literature" (
  "name" text,
  "deceased_spouse" text,
  "cause_of_death" text,
  "date_of_spouses_death" text,
  "length_of_marriage" text,
  "children_together" text,
  "current_marital_status" text
);
SELECT "cause_of_death" FROM "literature" WHERE "length_of_marriage"='28 years';