Answer:
The correct answer is option C
Step-by-step explanation:
In 1915, the RMS Lusitania, a British ocean liner, was sunk by a German submarine off the coast of Ireland. The sinking resulted in the loss of over 1,100 lives, including 128 Americans. This event, along with other instances of German submarine warfare targeting neutral ships, strained relations between the United States and Germany.
Although the sinking of the Lusitania played a significant role in increasing anti-German sentiment in the United States, it did not immediately lead to American entry into the conflict. It wasn't until 1917, when Germany resumed unrestricted submarine warfare, targeting both merchant and passenger ships, that the United States declared war on Germany. The sinking of American ships, including the SS Housatonic and the SS Illinois, further escalated tensions and pushed the U.S. towards involvement in World War I.
Therefore, the correct answer is 1917, as it was the sinking of the SS Lusitania and subsequent events that ultimately led to American troops entering the conflict.