Why did the united states support the nationalists in the civil war in china?

 the Nationalists had control of the major cities in the 1930s, and appeared to be the legitimate government of China. the United States began their support of Jiang Jie-shi and the Nationalists from 1941 on, as an ally against Japan in World War II. 
 

It is c because it shows how the author is stating their own oppinion about the protagonist