Which of these did the soviet union do in 1961?
a. it built a wall through berlin to keep people from moving to the west
b. use force to destroy a wall the united states had built in berlin
c. you convinced the british and french to merge their zones in berlin with the soviet union.
d. it's her into bomb for a loan if the united states did not leave within 30 days

The answer is: It built a wall through Berlin to keep people from moving to the West.

During that period, Germany's region was divided into two:
- Western Germany which was under democratic influence and an ally to the United States
- Eastern Germany, which was under communist influence and an ally to soviet union

since the condition of Western Germany was better than the East, many people started fleeing to the west. To prevent this, Soviet Union built the Berlin wall that separated the two regions.

The theory is land mass basically what they said.