Answer: A is correct
Explanation: After the end of the WW II there was a Conference in Jalta. In this conference European continent was divided in so-called "occupation zones". Berlin was divided as well - there were "western zones" (British, American and French) and a "Soviet zone" (Eastern Berlin). At that time there were no walls but the tension between ex-allies was increasing. After that two German republics were founded (1949). The growing tension led to blockage of the western Berlin: army, police and other military troops occupied the frontier dividing western and eastern Berlin in 1961. That was the materialization of so-called "iron curtain".
