Although the author does describe obstacles to community self-teaching, the focus of the passage isn’t on the idea that some tribes are having difficulty teaching traditional languages. Rather, the author focuses on the fact that some communities are engaged in self-teaching. The focus on the use of self-teaching as a way of preserving traditional languages, not on the difficulty that some tribes face in self-teaching.

Not supported, because the author never suggests that teaching traditional language is “necessary” in order to preserve tribal culture. Although some tribes have begun teaching traditional languages to help preserve those languages, this doesn’t imply that this kind of teaching is absolutely required in order to preserve tribal culture. Since (B) isn’t supported, it can’t be the main point.

The author doesn’t focus on tribes that use Western-style linguistics. Rather, the use of Western-style linguistics can cause difficulties in teaching traditional language, and the author points out that some tribes don’t use Western-style linguistics.

This best captures the main point, which is that some tribes are engaged in community self-teaching of traditional languages.

Not supported, because the author never suggests there’s an “inherent contradiction” in preserving oral culture in writing. Although the author notes in P5 that some people think oral languages don’t need to be written down, and that there can be difficulty in translating certain sounds into writing, this doesn’t imply that there’s some inherent incompatibility between oral languages and writing. In any case, the author also doesn’t indicate that some tribes are “sidestepping” a contradiction. They’re not necessarily evading difficulties involved in teaching traditional languages.