Answer:
A, the red scare
Explanation:
The red scare occurred after World War II when the fear of communism expanded across the US as the USSR grew and the Cold War gained steam.
The other three events took place after World War I. The KKK allegedly reorganized inspired by the movie "The Birth of a Nation" which premiered in 1915.
Agriculture and Mining suffered during the 1920s, forcing people to migrate to urban areas.
For a time, there were no more oil fields discovered, mainly due to the depth of the oil reserves and the lack of proper technology.