Answer:
d. after discovery of the Zimmermann Telegram.
Step-by-step explanation:
President Woodrow Wilson appeared before a joint session of Congress on the 2nd of April, 1917 to formally request a declaration of war against Germany.
The United States of America entered World War I (WWI) on the 6th of April, 1917 with its allies (Russia, France and Britain), only after Germany resumed an unrestricted submarine warfare against its passenger and merchant ships in the Atlantic and after discovery of the Zimmermann Telegram.
Zimmermann Telegram was a coded or secret diplomatic message sent on the 16th of January, 1917 from the German foreign office by secretary Arthur Zimmermann to the German minister in Mexico requesting for an alliance should the United States of America enter WWI against Germany.