TOEFL Reading: ETS-TOEFL阅读机经 - BR87U63PO1Z58Z77L$

Which of the following contributed to the success of the strategy discussed in paragraph 6? A. Crops were planted high enough to avoid being carried away by floods. B. Crops were planted wherever there were sources of water, regardless of their proximity to where people actually lived. C. Farming was limited to ecological zones that were similar to each other. D. Instead of aiming at becoming self-sufficient, each village became part of a network of diverse economic activities.