What is Realpolitik?

A.
the concept that political decisions of foreign engagement have to be based on the best interests of all parties concerned

B.
the concept that political decisions have to be made by consensus or new alliances should be sought out

C.
the concept that political decision about foreign engagement have to be based on preserving the interests of your country above all

D.
the concept that a single country, acting alone, has the most realistic chance of meeting its own needs