某研究机构利用水池(4m×2m×1m)、土壤、芦苇、水管等材料设计了一个人工湿地系统图。若用无植物的相同模拟系统实验，则检测到（    ）

    Most American families are smaller than the families in other countries.
Children in the USA will 1 their parents' home when they grow up. They usually live far from their parents because they often goo to different places to find good jobs. They often  2 to their parents or phone them, and they can choose their own 3.  Americans think it's important for young people to make their own decisions.
    Children are asked to do some house work at  4. In many families, children are paid for 5 the housework so that they can learn how to manage their own money.