TOEFL Listening: ETS-TOEFL听力机经 - VW99O51DGJMH5APYP$

What does the professor imply causes the eventual collapse of the Gara Monte's society? A. The region became overpopulated. B. The water tunnels that the Gara Mantes built fell apart. C. The water supply became contaminated. D. The underground supply of water was exhausted.