What is the IUNC of district of Cayo and reserve of Actun Tunichil Muknal?
CREATE TABLE "list_of_natural_monuments" (
  "reserve" text,
  "district" text,
  "iucn" text,
  "co_management" text,
  "est" real,
  "description" text
);
SELECT "iucn" FROM "list_of_natural_monuments" WHERE "district"='cayo' AND "reserve"='actun tunichil muknal';