Final answer:
Pope Pius XII signed the Lateran Treaty on behalf of Victor Emmanuel III, while Cardinal Gasparri signed on behalf of the pope.
Step-by-step explanation:
The Lateran Treaty was signed in 1929 between the Kingdom of Italy and the Holy See, which is the central governing body of the Roman Catholic Church. On behalf of Victor Emmanuel III, the King of Italy, the treaty was signed by Prime Minister Benito Mussolini. On behalf of the Pope, Cardinal Pietro Gasparri signed the treaty. Therefore, the correct answer is d) Pope Pius XII.