The passage suggests which one of the following about the historians mentioned? A. They have been unable to provide satisfactory explanations for the persistence of European ethnic communities in the United States. B. They have suggested that European cultural practices have survived although the community ties of European ethnic groups have weakened. C. They have hypothesized that European ethnic communities are based on family ties rather than on a sense of national consciousness. D. They have argued that European cultural traditions have been transformed in the United States because of the pluralism of American life. E. They have claimed that the community ties of European Americans are still as strong as they were when the immigrants first arrived.