Bismarck's "Reinsurance" Treaty with Russia Demonstrated Considerable Diplomatic Finesse Because

Bismarck's "reinsurance" treaty with Russia demonstrated considerable diplomatic finesse because:

A) Germany and Russia had been enemies earlier.
B) the Russian tsar hated Bismarck.
C) Russia and Austria were enemies in the Balkans, and Germany was also allied to Austria.
D) Bismarck sided with the Polish when they had revolted against Russian rule in 1863.