Answer:
C- unrestricted German attacks on ships
Explanation:
America entered WWI on April 2nd, 1917 after Germany attacked a series of submarines in the North Atlantic and the Mediterranean.
Germany started attacking a series of submarines around 1917 after they attacked a French submarine called Sussex, the US threatened to sever the diplomatic relations with Germany. They continued the attacks until they sank the British passenger liners Lusitania and Arabic killing 131 Americans. Germany continued to be a threat to the US until President Wilson decided to ask Congress for a declaration of war which was accepted.
