The most accurate analysis of why the Chinese Communists were victorious in the Chinese Civil War is:
The Chinese Communists were able to win the Chinese Civil War due to: a corrupt nationalist government, economic discontent, an inadequate nationalist military.
This response captures the key factors that contributed to the success of the Chinese Communists, including the corruption and inefficacy of the Nationalist government (Kuomintang), widespread economic hardship among the populace, and the weaknesses of the Nationalist military compared to the better-organized and more ideologically motivated Communist forces.