题目

We’ve talked about snails (蜗牛) and their slow move. But much of the time snails don’t move at all. They’re in their shells ---sleeping . Hot sun will dry out a snail’s body. So at the least sign of hot sun, a snail draws its body into its shell and closes the opening with a thin cover. Then it goes to sleep. A snail will die in a heavy rain. So whenever it rains, it goes inside its shell house and goes to sleep. A snail can sleep for as long as it needs to. It can take a short sleep. Or it can sleep for days at a time. And it spends all the winter months in its shell, asle试管中有少量黑色混合粉末，加热一段时间后，黑色粉末变红，将产生的气体通入澄清石灰水，石灰水变浑浊。   (1)黑色粉末的成分是-------------------。   (2)发生反应的化学方程式是------------------------。   (3)实验结束后不久，试管中红色物质又变成黑色。出现这一现象的原因是--------------。