Which of the following assesses Germany's use of unrestricted U-boat warfare? (1 point)
A. • Germany's use of unrestricted U-boat warfare expanded the war and eventually caused the U.S. to declare war on Germany.
B. • Unrestricted U-boat warfare had little effect on the war.
C. • Unrestricted U-boat warfare damaged British shipping, but didn't have further consequences.
D. • Unrestricted U-boat warfare forced the British to sue for peace.