TOEFL Listening: TPO-TOEFL阅读TPO - 0F83212251T410G0N$

In paragraph 6, the author discusses "The thriving obsidian operation" in order to A. explain why manufacturing was the main industry of Teotihuacán B. give an example of an industry that took very little time to develop in Teotihuacán C. Illustrate how several factors influenced each other to make Teotihuacán a powerful and wealthy city D. explain how a successful industry can be a source of wealth and a source of conflict at the same time