题目

下列哪一生态系统被誉为“地球之肾” A.湿地生态系统    B.草原生态系统    C.森林生态系统    D.湖泊生态系统 答案：AWhen she heard her name called, she looked __ the newspapers. A. away from　　 B. out for　　　　 C. up for　　　　 D. up from