Answer:
B) The sinking of the Lusitania.
Step-by-step explanation:
The RMS Lusitania was a British ship that was sunk by a German U-boat on May 7, 1915, off the coast of Ireland. The ship was not armed, and was carrying thousands of civilians. Moreover, 128 American citizens were found among the dead. After this event, public opinion in the United States became extremely anti-German, and this eventually led to the United States joining WWI.