Answer is B U-Boat activity
The us entered world war 1 on April 6, 1917
They reacted by having everyone work in the industry. While the men were fighting the war or making things that support the war, the women were also involved in production of weaponry and supplies. Even the children joined the war effort as Hitler's Youth, which was like a program for children to join the support of the government. When things got really serious and dangerous they even sent the children to fight.
D. Has changing conditions as the ocean alternates between high and low tides.
Im thinking maybe latin america and asia i could be wrong though
