Final answer:
The reaction to the Red Scare was the Palmer Raids, which targeted newspaper presses, immigrant groups, and Russian worker unions. Therefore, the correct option is a. Palmer Raids
Step-by-step explanation:
The reaction to the Red Scare in the United States was the Palmer Raids. Attorney General A. Mitchell Palmer authorized the raids, which targeted newspaper presses, immigrant groups, and Russian worker unions, and resulted in the arrest and deportation of supposed 'radical aliens'. The Palmer Raids demonstrated the government's power to ignore individual rights and led to the formation of the American Civil Liberties Union in 1920.