Why Did World War I Transform Western Civilization So Profoundly

Why did World War I transform Western civilization so profoundly?

A) The mass slaughter of World War I was hard to reconcile with the optimist claim that Western civilization was the triumph of reason and human progress.
B) Since a vast majority of victims were civilians, the war forever changed public perceptions on the acceptability of military conflict.
C) As a global conflict between socialist nations on the one hand and monarchies on the other, the war signaled the ideological divisions of the twentieth century.
D) The war generated an economic boom in Europe and the United States that marked the beginning of the so-called Roaring Twenties.