C? What effect did the entry of the United States into World War I have on the course of the war? It pushed Russia out of the war. It opened a new front in the fighting. It helped bring a quick victory to the Allies. It led to a large number of causalities on both sides.
"It led to a large number of causalities on both sides" would be the best option from the list, since the war still dragged on although now with far more men involved, meaning more deaths.
