Answer:
B. the sinking of the Lusitania and the Zimmermann Telegram
Step-by-step explanation:
When Germany attacked a British ship, the Lusitania, over 100 Americans were killed. This event greatly angered many Americans.
Later, in 1917, a message from Germany to Mexico was found. It asked Mexico to declare war on the U.S. This message, called the Zimmermann Telegram, was published in the U.S. and turned many Americans against Germany. The U.S. declared war on Germany on April 6, 1917.