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 French stopping the German advance in the west at the First Battle of the Marne in September 1914 led to trench - warfare which extended the war into 1915 and beyond. The Americans entered in 1917, the Russian Revolution was in 1917 and the Russian stop of German advance didn't extend the war in the way the French action did.

Answer:

The French stopped the German advance in the west.