Question

when world war i began in august 1914, many people anticipated that the war would end by christmas of that year. which event extended the war into 1915 and beyond?
the americans entered the war.
the french stopped the german advance in the west.
the russian revolution expanded the war in the east.
the russians stopped the german advance in the east.

Explanation:

The question asks which event extended WWI beyond 1914. The American entry (1917) was too late; the Russian Revolution (1917) led to Russia exiting the war, not expanding it; the Russian stop of German advance in the east was not a key early war-extending event. The French stopping the German advance at the First Battle of the Marne (September 1914) halted Germany's Schlieffen Plan, preventing a quick victory and leading to trench warfare that prolonged the war into 1915 and beyond.

Answer:

The French stopped the German advance in the west.