During world war i, the western front in europe was characterized by a) trench warfare. b) constant movement of troops. c) unrestricted submarine warfare. d) the breakdown of the russian defense.

A)trench warfare.

It is not B, because there was large amount of stale mates, which led to the war dragging on for a long time
It is not C, because the western front in Europe typclified land, and not sea.
It is not D, because the Russian forces were located in the Eastern side, not the Western.

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