Final answer:
The correct statement about the Eastern and Western Fronts during World War I is that they were witness to equally terrible casualties. The Eastern Front was more mobile, whereas the Western Front was characterized by static trench warfare, both resulting in high fatality rates.
Step-by-step explanation:
The Eastern and Western Fronts during World War I were markedly different in terms of their military dynamics. The Eastern Front was characterized by greater mobility, with the fighting involving rapid maneuvers and sometimes vast movements across territory, as the Russian, German, and Austrian armies attempted to outflank one another. In contrast, the Western Front was known for its entrenched, static form of warfare, with both sides entrenched in a protracted and often immovable trench system.
While the Eastern Front did see the Russian army effectively engaging against Austrian forces, and surprising the Germans with their quick mobilization, they suffered from an inadequate industrial base, insufficient railways, and eventually massive attrition. The Western Front, on the other hand, turned into a stalemate with continuous attempts to break each other's lines, leading to a grueling form of trench warfare.
Given this information, the statement that most accurately describes the nature of the Eastern and Western Fronts is option 3: C, witness to equally terrible casualties. Both fronts endured massive losses, with hundreds of thousands of soldiers dying in the battles such as the Brusilov Offensive on the Eastern Front and the trench stalemates on the Western Front.