The author refers to the fact that adult "Harris sparrows" are usually dark throated, in order to do which one of the following? A. support the conclusion that plumage variation among Harris sparrows probably does not signal individual status B. argue that plumage variation among Harris sparrows helps to confirm the status signaling hypothesis C. indicate that in light of plumage variation patterns among Harris sparrows, the status signaling hypothesis should probably be modified D. demonstrate that Harris sparrows are the most appropriate subjects for the study of status signaling among birds E. suggest that the signaling of age-related differences in status is widespread among birds that form flocks