What did russia do to stop people from leaving east berlin?

After World War 2 Germany was dived into half. The western half was under American control and the Eastern half was under Russian control. Berlin lay in the Western half and was divided between Russia and America, meaning that East Berlin was an island of Russian controlled Germany surrounded by areas under American control. Russia was a communist country and people from East Berlin tried to flee to West Berlin and so the Berlin Wall was built to stop this.Until the east Germans were rescued by pink Floyd!

Your answer is 2 because you do keep change flip when you divide fractions