Answer:
A. The weather.
Explanation:
Russia had two greatest invasions, the French under Napoleon´s command and the German under Hitler´s orders.
Both invasions gained several portions of the Russian soil but failed to convince the Russians of surrender against them. Both invasions were planned to be fast with a large number of troops but they never counted on the strength and resistance of the Russian army. The attacks took larger than expected and when the winter arrived both armies suffered the cold and ended withdrawing their forces.
I hope this answer helps you.
