The correct answer is A. The major outcome of the Battle of Britain was that German troops were forced to continue fighting the Allies in Western Europe, as they couldn't take all the territory, with England remaining on the allied side.
The Battle of Britain was the first great battle entirely contested in the air. It was the largest and busiest air campaign to date and the first test of the bombing strategies that emerged since the First World War and it was also the first time during WWII that Germany was defeated. This defeat supposed that, when Hitler invaded the USSR in 1941, Germany would fight in a war with two fronts open at the same time, contradicting his ideas exposed in Mein Kampf, in which he exposed the geographical disadvantage of Germany, positioned among the Western democratic powers (like the United Kingdom and France) and the socialist government of the USSR, with respect to other powers and therefore should never fight a war without first closing a front before opening another.