I’d hate to be wrong, but it might be the last one.
The best answer is Europe anti communist efforts.
The construction of the Berlin Wall is often thought of as a result of the Cold War between the United States and the USSR. To an extent, this may have some truth to it, but the most significant reason was the massive number of anti-communist people in East Germany leaving the Soviet-controlled country through Berlin. The USSR needed a way to plug up this hole, so they constructed the wall.
I think that the best answer is letter A
