The correct answer is Both B and C.
The sinking of the Lusitania in 1915 by a German U-Boat, which resulted in the deaths of many Americans, and the Zimmerman Telegram in early 1917, in which Germany sought a military alliance with Mexico against the United States, were significant factors that contributed to the U.S. decision to enter World War I. The sinking of the Titanic, while a notable event, was not a direct reason for U.S. entry into the war.