The water we drink and use was running short. We all have to learn what to stop wasting water.

One of the step that we should take is to find ways of reusing it. Today in the most large cities, fresh water is used only once and then it runs in waste system. But that is possible to pipe the used water to a purifying factory, there the used water can be treated with chemical materials by the workers so that it can reused. But even if every large city purified and reused it's water, we still would have enough water.   

学生甲把石灰石装入试管时，不慎打破管底，其原因可能是：______，后来学生乙用这支底部有破洞的试管和一个广口瓶组装成制取二氧化碳的发生装置（如图所示）．在铜网上应盛放______，广口瓶中应盛入______．两种药品发生反应的化学方程式为______．