Which one of the following best expresses the main idea of the passage? A. The socioeconomic achievement of Chinese and Japanese immigrants and their descendants is best explained by a historical examination of the economic structures prevalent in the United States when such immigrant groups arrived. B. The socioeconomic achievement of Chinese and Japanese immigrants and their descendants is best explained by an examination of their cultural backgrounds, in particular their level of educational attainment. C. The socioeconomic achievement of Chinese and Japanese immigrants and their descendants has taken place in the context of a culturally based emphasis on the economic welfare of the nuclear family. D. Only the market structure of the capitalist economy of the United States in which supply has historically been regulated by demand can account for the socioeconomic achievement of Chinese and Japanese immigrants and their descendants. E. Only an analysis that combines an examination of the culture of Chinese and Japanese immigrant groups and the socioeconomic structure of the host country can adequately explain the socioeconomic achievement of Chinese and Japanese immigrants and their descendants.