What Was the Nature of the Russian Resistance to the Mongol

What was the nature of the Russian resistance to the Mongol invasion?

A) The Russian cities allied rapidly to confront the Mongols with a united force.
B) As the leading commercial centers of Russia, Kiev and Novgorod allied to create a substantial military force that saved those cities from destruction.
C) The Russians appealed to the Byzantine Empire to provide them with military assistance against the Mongols.
D) The princes of Russia refused to cooperate and were routed individually.