Final answer:
Senator Joseph McCarthy and the House Un-American Activities Committee (HUAC) contributed to the Red Scare by accusing American citizens of being communist spies, making option a. McCarthy/HUAC' the correct answer.
Step-by-step explanation:
The individual/group that contributed to the Red Scare by accusing American citizens of being communist spies were Senator Joseph McCarthy and the House Un-American Activities Committee (HUAC). Therefore, the correct answer is a. McCarthy/HUAC. McCarthy was notorious for his role in fueling the fears of communism in the 1950s by making public accusations without providing proper evidence, which led to the term 'McCarthyism,' referring to the intense anti-communist suspicion. The HUAC also played a significant role by investigating alleged disloyalty and subversive activities on the part of private citizens, public employees, and organizations suspected of having communist ties.