Answer:
Hold on at all cost and stop Russia from invading eastern Germany.
Step-by-step explanation:
The plan to fight Russia in the east while the Germans attacked France in the west is widely known as Schlieffen's plan.
The plan was based on many factors, among which was France was the enemy to be conquered early, with Russia contained or hold on until the French were eliminated.
Hence, in this case, the correct answer is "Hold on at all cost and stop Russia from invading eastern Germany."