According to paragraph 4, what was part of the explanation for the shift away from humor toward greater formality in popular illustration? A. Many of the comic journals of the earlier period had either failed or cut back on the number of illustrations they published. B. Mainstream popular magazines had begun including articles on serious subjects. C. The mood of the times had become less lighthearted and more concerned with respectability. D. The most respected illustrators had become unwilling to use imagination as a basis for their work.