Between the mid-1930s and the end of World War II, A) Chiang Kai-shek finally obtained a firm grip on all but northwest China, and implemented a "crash program" of modernization, which won peasant support. B) the Chinese Communists steadily increased their power in the north until, by 1945, between twenty and thirty million people were under their control. C) Japan made peace with Chiang in 1940, joining him in a war against Mao's Communists. D) Mao Zedong married Chiang's daughter, which reunited China until the late 1950s. E) the Chinese Communist party changed its focus from organizing peasants to winning over the middle-class city dwellers and the large bankers in Shanghai.

(B) the Chinese Communists steadily increased their power in the north until, by 1945, between twenty and thirty million people were under their control

Explanation: The chinese communists are the ruling party in the people's republic of China. The party was formed in 1921 and by the end of the civil war, it had amassed millions of followers had driven the Kuomintang's nationalist government from mainland China, leading to the establishment of the People's Republic of China. The Communist party of China (CPC) is the sole governing party in mainland China and it also controls the People's Liberation army which is the world's largest armed forces.

The KMT and CPC often had to join forces to work together but despite their formal alliance, the CPC used the opportunity to expand and carve out independent bases of operations to prepare for the coming war with the KMT which garnered them support that helped in eventually driving out the KMT after World War II ended.