TOEFL Listening: ETS-TOEFL听力机经 - 0IOX6383IQ6M33D4P$

What does the professor imply about property deeds in Tlingit clans? A. They existed in non-written forms. B. They were often difficult to enforce. C. They were not officially recognized by other native American groups. D. They were a major source of conflict between Tlingit clans.