challenge: What was Nakhchivan's role in the trade of obsidian in the Lake Urmiah basin?
  
  A. Nakhchivan had no involvement in the trade of obsidian
  B. Nakhchivan was the primary consumer of the obsidian
  C. Nakhchivan was the source of the obsidian deposits
  D. Nakhchivan was the intermediary in the trade of obsidian
  Answer: 