题目

Our family enjoyed a beautiful house plant for over thirty years. It had stayed with us through ________ years and good times, pain and joy. I had never thought of ________ it.However, two weeks ago, we ________ some changes of its leaves, which began to lose its color. We watered and looked after it even to the point of ________ it, like a child. But it just showed no sign of ________. We finally picked a few almost dead leaves and ________ replanting them in another small pot.What ________ us was that these leaves which had been planted in the new pot grew strong. In order to know the reason（4分）如图，在实验台上放置两瓶气体，集气瓶A盛有CO2、O2、H2中的一种，集气瓶B盛有这三种气体中的另一种。小刚和小强想对瓶中气体进行探究。（1）他们由放置方法判断， A瓶中的气体是       ；（2）小刚和小强分别设计如下探究方案，都能确定B瓶气体是余下两种气体中的哪一种。小刚的方案：将燃着的木条伸入B瓶中，观察现象。按小刚方案实验时，若木条火焰熄灭，则B瓶中的气体是       ；小强的方案：将一种无色溶液倒入B瓶中，振荡，观察溶液是否发生明显变化，所选的无色溶液是              ，化学反应方程式为                         。