The correct answer is - A. Prussia.
Otto von Bismarck is one of the most important figures in the more recent German history. He was the one that managed to unify the smaller German states. Otto von Bismarck gained control over Prussia, the largest and strongest of the Germanic states. He had a vision that all German states should be unified, and that a strong German nations should be formed. Step by step he managed to unite the German states, thus forming a united German nation for the first time in history. But he didn't stopped there, he wanted to incorporate all the territories where Germanic people lived, thus he waged wars against France, Austria, and Denmark, with mixed success.