Final answer:
Food shortages and participation in an unpopular war were the main factors that led to communist revolutions.
Step-by-step explanation:
The correct answer is A. Food shortages, and participation in an unpopular war. In the 1930s, several factors contributed to the rise of communist revolutions. One of the main factors was food shortages, which created discontent among the population. Additionally, participation in unpopular wars, such as World War I, further fueled the desire for radical change. Communism offered an alternative to the capitalist systems that were failing during the Great Depression, promising economic equality and a classless society. The appeal of communism grew among those who felt abandoned by the capitalist system and saw communism as a solution to their economic hardships.