What Was Somewhat Unique in Warfare Regarding the Battle of Britain

What was somewhat unique in warfare regarding the Battle of Britain?

A) It was fought entirely in the air and was a clear victory by the British.
B) It allowed the British to test secret jet aircraft against the Germans.
C) It was fought entirely underwater with German and British submarines.
D) The British were able to stop the German invaders on the shores of England.
E) The Germans kept the British from invading their homeland by use of armored vehicles.