(A) the Sussex Pledge
(B) ** the interception of the Zimmerman telegram
(C) the sinking of the Lusitania
(D) unrestricted submarine warfare
EXPLANATIONS BELOW
Concept note-1: -In January of 1917, British cryptographers deciphered a telegram from German Foreign Minister Arthur Zimmermann to the German Minister to Mexico, von Eckhardt, offering United States territory to Mexico in return for joining the German cause.
Concept note-2: -The Zimmermann Telegram (or Zimmermann Note or Zimmerman Cable) was a secret diplomatic communication issued from the German Foreign Office in January 1917 that proposed a military alliance between Germany and Mexico if the United States entered World War I against Germany.
Concept note-3: -On January 17, 1917 British signals intelligence intercepted and decrypted a coded German telegram from German Foreign Secretary Arthur Zimmermann that was intended for Germany’s ambassador to Mexico.
Concept note-4: -This roundabout route was used because Germany no longer had cables in the Atlantic and because there was no direct wire from Denmark to the United States. Therefore, the message was sent from Copenhagen to a relay station on the westernmost point of England, where it was intercepted by the Room 40 codebreakers.