What date did the prime minister who entered office on 7 December 1916 leave office?
CREATE TABLE "prime_ministers" (
  "name" text,
  "entered_office" text,
  "left_office" text,
  "political_party" text,
  "monarchs_served" text,
  "birth_place" text
);
SELECT "left_office" FROM "prime_ministers" WHERE "entered_office"='7 december 1916';