Why Is the Battle at Fort Donelson Significant

Why is the battle at Fort Donelson significant?

A) It was the site of a major battle east of the Appalachian Mountains, where most militarily significant early battles took place.
B) It was an important Union fortification on the Great Lakes that caused the Civil War to extend all the way into Canada.
C) It ensured that Kentucky would fall to the Confederacy and would begin to institute the system of slavery as part of its new economy.
D) It was the site of one of the first major Union victories, as the most important early battles in the war had happened in the West.
E) It guaranteed that the Confederacy would maintain full control of its river system, including the Cumberland and Tennessee Rivers.