To determine why Eastern American Indians were generally more adaptable to the "civilizing" influence of Christian missions compared to Plains Indians, we need to consider the historical, cultural, and social factors that might have influenced their level of adaptability.
First, let's examine option A: Eastern American Indian belief systems resembled Christianity much more than Plains Indian belief systems, which tended to be atheistic. While it is true that some American Indian tribes or groups had belief systems that differed from mainstream Western religions like Christianity, it is inaccurate to generalize the entire Eastern American Indian population as having belief systems resembling Christianity. Different tribes and groups had diverse religious and spiritual practices, which might have shown similarities to Christianity in some cases but not in others. Therefore, option A might not be a comprehensive explanation for the greater adaptability of Eastern American Indians to Christian missions.
Moving on to option B: Eastern American Indians had been in consistent contact with whites much longer than Plains Indians, who only met whites sporadically in trading. This option is a more plausible explanation. Eastern American Indian tribes had the longest contact with Europeans due to colonization, early settlement, and long-established trade networks. This prolonged contact exposed Eastern tribes to European culture, including Christianity, over an extended period. As a result, Eastern American Indians might have developed a higher level of familiarity, understanding, and adaptability towards Christian missions.
Regarding option D: Eastern American Indians had developed reading and writing skills, and Plains Indians used only spoken language. While the ability to read and write could potentially contribute to adaptability towards Christian missions, it is important to recognize that not all Eastern American Indian tribes had universal literacy or widespread use of written language. Additionally, Plains Indian tribes had oral traditions and rich storytelling cultures, which were equally valuable but relied on spoken language rather than writing.
Considering the information provided, option B is the most likely reason for the greater adaptability of Eastern American Indians to Christian missions. Their longer exposure and consistent contact with whites, including missionaries, allowed for more interaction, familiarity, and potential acceptance of Christian teachings and practices. It is important to note that generalizations cannot fully capture the diversity within and between American Indian tribes and that individual experiences and cultural factors also played significant roles in their responses to Christian missions.