TOEFL Listening: ETS-TOEFL听力机经 - E5W3S43CBC77MZ8CP$

According to the professor, why did Tlingit potlatches always include guest clans? A. The presence of multiple clans was display of respect to the chief of the host clan. B. Multiple clans ensured that a large number of items would be available for exchange. C. Individual clans were not large enough to have their own potlatch. D. The presence of outside witnesses validated changes within the host clan.