The statement that accurately compares the Eastern and Western Fronts is:
The Western Front had flat terrain, whereas the Eastern Front had mountains, valleys, rivers, and forests.
This statement captures the geographical differences between the two fronts during World War I. The Western Front, primarily located in France and Belgium, was characterized by trench warfare on relatively flat land, while the Eastern Front, which spanned areas including parts of Russia, was more diverse in terrain with various geographical features.