Answer:
Part (a) → Just to give a bit of background, the Berlin Wall divides the West and East side of Germany. The main reason why this wall was built was to prevent people from escaping Soviet-controlled East Berlin to West Berlin which was controlled by the Western Allies. It was built by the German Democratic Republic during the Cold War.
Part (b) → Many people from East Berlin were escaping to West Berlin which was controlled by the west to which the Soviets didn't like and responded with building a wall. The reason what caused the migration of people was because of the horrendious doctrines that were put in place in the East.
Part (c) → The fall of the Berlin wall signified the end of Cold War.