The correct answer was A) it wasn't necessary to rebuild land and industries.
The primary reason for the economic boom that occurred in the United States after World War II was that it wasn't necessary to rebuild land and industries.
European countries such as Germany were devastated during World War II. Other countries such as England and France were severely damaged due to the air raids and army invasions during the war. Some cities were destroyed and all of them needed reconstruction. But that was not the case of the United States. America did not need any reconstruction. Furthermore, the United States implemented the Marshall plan to help reconstruct Europe. So it is true that the primary reason for the economic boom that occurred in the United States after World War II was that it wasn't necessary to rebuild land and industries.