水是生产生活中必不可少的物质，请你回答下列有关水的问题：

（1）生活中常用的降低水硬度的方法是____．

（2）自来水厂净水的方法有：沉降、过滤、活性炭吸附、消毒等，其中属于化学变化的是____ ．

（3）珍爱水资源是每个公民应尽的责任和义务，从自身做起，生活中你能做到的节水方法是____ （答出一点即可）．

任务型阅读

    My name is George．I'm from England．Now I'm studying in Germany．I get to school at 7：30 every morning．I find many of my schoolmates come to school by bike．  ①   

    This is an interesting thing for me．In England people usually drive，take a bus or walk somewhere，for example，to school．In Germany, I often see people，even people over eighty years old going somewhere by bike．It makes me think：  ②   

My father gives the answer．We are living in Northern Germany．It is very flat(平坦的).So it is easy for people here to go somewhere quickly by bike .And it's cheaper than(比…….便宜)going by car or by bus．Also,it's good for the environment(环境)．

    I like riding bikes now．   ③    When I go back to England，I will ride more and ask my friends to ride with me．I think they will like tiding bikes，too．

根据材料内容完成下列任务。

游乐园的小朋友从滑梯匀速下滑过程中，小朋友的动能____，小朋友的机械能总量____．（选填“变大”、“变小”或“不变”）若该小朋友用5s的时间，从长15m的滑梯匀速滑下，小朋友的速度是____ m/s．