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    There are many apple trees in a garden. They're good friends. One day an old tree is ill. There are many pests in the tree. Leaves of the tree turn yellow. The old tree feels very sad and unwell. Other trees send for a doctor for him. At first, they send for a pigeon, but she has no idea about it. Then they send for an oriole(黄鹂), and she can't treat the old tree well either. Then they send for a woodpecker. She is a good doctor. She pecks a hole in the tree and eats lots of pests. At last the old tree becomes better and better. Leaves turn green and green.

从革命性质分析，俄国革命实际上经历了三种革命：即发生在彼得格勒和莫斯科等工业中心的无产阶级革命，发生在广大农村的以农民夺取土地为主要方式的农民革命，发生在民族地区的民族革命。最终，力量弱小的布尔什维克党赢得并巩固了政权。据此判断，俄国革命的成功主要是由于无产阶级（    ）

请你设计蜡烛变化的实验，将实验步骤补充完整

材料：蜡烛、烧杯、澄清的石灰水、三脚架、酒精灯、燃烧皿（白瓷）、石棉网等。

步骤：