The Treaty of Versailles was the peace agreement that formally ended the First World War between Germany and the Allied Powers. Although the armistice that halted fighting was declared on 11 November 1918, the treaty itself was not ready for signing until the following year.
Negotiations began at the Paris Peace Conference in January 1919, led primarily by the "Big Four": Woodrow Wilson of the United States, David Lloyd George of Britain, Georges Clemenceau of France, and Vittorio Orlando of Italy. After months of deliberation over territorial adjustments, reparations, military restrictions, and the creation of the League of Nations, the final text was presented to Germany.
The treaty was signed on 28 June 1919 in the Hall of Mirrors at the Palace of Versailles, France. The date was chosen deliberately: it was exactly five years after the assassination of Archduke Franz Ferdinand, the event that triggered the war.
The correct answer is therefore 1919. The year 1918 marks only the armistice, not the treaty. The years 1920 and 1921 fall after the signing, though some other post-war treaties (such as the Treaty of Trianon in 1920 and the Treaty of Riga in 1921) were concluded in those years.
Exam tip: Distinguish between the armistice (November 1918) and the formal treaty (June 1919). Questions on the Treaty of Versailles almost always test the 1919 signing date.