GRE考试

【单选题】The primary purpose of the passage is to


A．expose the fragile ecological conditions which modern irrigation technologies must ameliorate
B．argue that new irrigation technologies would ultimately be less efficient than a reconfiguration of the North American diet
C．argue that efficient water-use is dependent upon a mixture of various modern methods
D．provide an overall view of possible methods for lessening the strain on sources of freshwater
E．(E) describe the cycle by which aquifers are depleted and then replenished through technology