The correct answer is: b) Oral traditions.
Many languages in Arunachal Pradesh do not have a written script, relying on oral traditions. This means that the language is passed down through generations by word of mouth, rather than being written down. This can make it difficult to preserve the language, as it can be easily changed or lost over time. However, oral traditions can also be a valuable way to preserve a language, as they can contain a wealth of information about the culture and history of the people who speak it.
Option a) is incorrect because Roman script adaptations are not the only way to write a language. There are many other writing systems that can be used, such as the Devanagari script or the Arabic script.
Option c) is incorrect because ancient pictographic systems are not commonly used in Arunachal Pradesh. Most of the languages in Arunachal Pradesh are spoken by small groups of people, and there is no one standard writing system for all of them.
Option d) is incorrect because neighboring languages are not always used for documentation of languages in Arunachal Pradesh. In some cases, linguists have developed their own writing systems for these languages.