TOEFL Listening: ETS-TOEFL听力机经 - S3O18A_35514TM1DP$

What does the professor imply about the terrace and the irrigation support of the Inca in the 1200s and 1300s? A. They were built primary to help the Inca survive a long drought. B. They were partly responsible for a rapid increase in the Inca population. C. They eventually helped the Inca maintain control over people. D. They eventually enabled the Inca to grow crops that were not native to Cuzco area.