Hey Haewon!!
That's great news! I'm glad to hear you are consistently studying! I'm so proud of you =). Are you also taking offical SAT practice tests? If not, make sure you do because the official tests are the most relevant to the actual SAT. =)
To your question...
You should not consider a specific explanation that is directly on-topic to be too concrete. Plus, thinking something is too concrete is subjective, right? And we don't want to be subjective on the test. So instead, let's stick to objective facts! =)
(D) states "allowed tribal elders"....objectively speaking, the tribal elders are the people in charge, which means they are responsible for peace, order, taking care of people, etc... And...if you look at the sentence before the example, it says "ceremonial objects had a role in resolving disputes and maintaining justice". These are things that fit with tribal elders. That is what makes (D) clear and correct. The ancestral spirits fit in line with the spiritual nature of the Igbo people (context of the passage). Anyways...can you see how (B) now is TOO general and that (D) is directly related to the topic in the passage? I hope so!!
Keep moving forward! You got this!