He invasion of hungary in 1961 by the soviet union and the building of the berlin wall in 1961 are examples of (1) united nations security council resolutions (2) truman doctrine failures (3) marshall plan effects (4) cold war era conflicts

 The correct answer is D or four

cold war era conflicts
  The Berlin conflict reached its peak when the soviet union, with the bid to stop migration of eastern Germans population to the west Germany controlled by the capitalists enacted the iron curtain. The soviet union also invaded Hungary to enforce its communist market ideas.