TOEFL Reading: ETS-TOEFL阅读机经 - JYC3G041WQWF7F83L$

All of the following are mentioned in paragraph 2 as potential problems faced by the Hohokam EXCEPT A. insufficient rainfall to allow crops to grow B. rainstorms leading to destructive water runoff C. insufficient workers to dig ditches and canals D. irrigation water levels in channels too low to be used