Answer:
The correct answer is C. One effect of unrestricted German submarine attacks on shipping in World War I was that the United States moved closer to declaring war on Germany.
Step-by-step explanation:
Underwater warfare during World War I was in part a struggle between the German U-Boats and supply convoys across the Atlantic bound for Great Britain. The British and allied submarines carried out a wide spectrum of operations in the Baltic Sea, the North Sea, the Atlantic Ocean, the Mediterranean Sea and the Black Sea. Only a few actions took place outside the North Atlantic. Attacks by German submarines on Allied merchants gave the Americans a direct reason to enter the war in April 1917, after the sinking of the Lusitania and the interception of the Zimmermann Telegram.