Why Did King Wilhelm of Prussia Assume the Title of "Kaiser

Why did King Wilhelm of Prussia assume the title of "Kaiser" at the conclusion of the Franco-Prussian War?

A) It was an old family name that he preferred because it emphasized consistency and tradition.
B) Derived from the Roman Caesar, the title represented the establishment of the German Empire.
C) The other states involved in the war stipulated during negotiations that because he had lost, Wilhelm had to take a new title.
D) The French demanded that Wilhelm take a title more aligned with French tastes.
E) He preferred it because "Kaiser" is the German word for "general' and emphasized his participation as a soldier.