Answer:
d. cut merchant marine losses greatly.
Explanation:
In 1917, Germany unleashed an unrestricted submarine war around the waters of Europe, which would bring the United States into the war.
Allied losses totaled more than 2.7 million tons. Nevertheless, the effort was not enough to beat the allies who had adopted a more efficient train system against the U-Boot; With it, about 2 million US soldiers were transported to the front, as well as weapons and supplies from Europe.
