31.12 Why were eastern American Indians more adaptable to the "civilizing" influence of Christian missions while plains Indians were less adaptable? A. Eastern American Indian belief systems resembled Christianity much more than Plains Indian belief systems, which tended to be atheistic. B. Eastern American Indians had been in consistent contact with whites much longer than Plains Indians, who only met whites sporadically in trading. C. Eastern American Indians had abandoned hunting practices for farming before European contact, while Plains Indians continued hunting. D. Eastern American Indians had developed reading and writing skills, and Plains Indians used only spoken language.