The old city of Koenigsberg, which had a German majority population before World War 2, is now called Kaliningrad
This line clearly shows that Kaliningrad was historically German
option C) Don't just assume anything. No where it is mentioned why was the past name changed and what is the significance of the new name or it's origin.
option D) Again no information about path which is b/w Russia and this kaliningrad. Why only this path why can't be Baltic sea?
option B) It is clearly mentioned that this Kaliningrad is surrounded by different countries like Lithuania and Poland so that means it is apart from rest of Russia.
Only option B can be inferred.