Answer:
B attack on Pearl Harbor
Step-by-step explanation:
the Zimmerman Telegram was when the German Empire sent a telegram made by Zimmerman to Mexico to try and get them to fight the USA to keep them from joining the Entante, that was WW1 so it's unrelated to ww2.
seeking of the Lusitania happened years prior and was appropriately reparated by the Japanese.
Germany invading Poland happened in 1938 so if it was really a big event to America which it wasn't they would have joined in 1938 instead of 1941