第十二届全国人大常委会第二十五次会议2016年12月25日审议通过了《中华人民共和国环境保护税法》的决定，并将于2018年1月1日开始实施。材料主要说明（    ）

    Do teenagers in small villages do chores at home? How about the teenagers in big cities? Here is a survey. We asked 4,000 teenagers in China several questions. Half of them come from big cities like Beijing, Shanghai and Guangzhou. The others are from small villages. We made a diagram of the result of our survey. Let's have a look at it. We found out that teenagers from small villages do more chores than those from big cities. Maybe it is because they live a harder life. Our advice to parents in big cities is that parents should give their children some chores to do. Doing chores teaches teenagers to take care of themselves.

    Chores 2000 teenagers in small villages.

    Chores 2000 teenagers in big cities

清洗内壁沾附碱性固体残留物试管的合理步骤是（   ）