A．Teotihuacan, once the home of 200,000 people, was the center of a large empire.
B．Many archaeologists are fascinated by the ruins of a pre-Columbia city called Teotihuacan.
C．Teotihuacan, once a major metropolitan area, was destroyed by an invasion.
D．A still unsolved mystery is why the people of Teotihnacan suddenly abandoned their city.