The answer would be D, creating a League of Nations. In order to prevent another world war, President Wilson thought that it would be best to create an international body with representatives from different nations, so that countries could discuss their problems rather than fight over them. This condition was added to the Treaty of Versailles, which the Central Powers were forced to sign.
Interesting fact, by the way: Although US President Wilson was the one to suggest creating the League of Nations, after the League was created, The United States did NOT join the League. This was because Wilson did not agree with the terms in the Treaty of Versailles. Wilson thought (correctly, as it turned out) that being harsh with the Central Powers would only lead to a future war.
