题目

 具有净化水源、蓄洪抗旱作用，被称为“地球之肾”的是（ ）A． 农田生态系统 B． 湿地生态系统 C． 草原生态系统 D． 湖泊生态系统 答案：B10. (2015 •广东佛山) I don't understand why more girls to do housework than boys in today's society.   A. asked   B. were asked   C. are asked