During his re-election campaign in 1916, president woodrow wilson used the slogan, "he kept us out of the war." in april, 1917, wilson asked congress for a declaration of war on germany. what explains the reason for this change?
a) britain was invaded by nations of the central powers.
b) german forces had invaded poland and belgium.
c) germany had resumed unrestricted submarine warfare.
d) russia signed a treaty of alliance with the german government.