Leon was a postman. Every day after Leon woke up, he would feed his 37 cats. Leon didn't really want 37 cats, but one by one they had turned up on his doorstep, and Leon had taken them in.

    Every day, after feeding the cats, Leon would collect the mail from the red postboxes in the village and take it home to sort（分类）. “If only I had 37 helpers instead of 37 cats, my job would be so much easier,” Leon thought. Just then, the cats started meowing for their dinner. That gave Leon an idea. That night, Leon stayed up making 37 cat-sized postal backpacks. Each backpack fitted neatly onto a cat's back. Then, he went around to each postbox, putting signs up that read: Postbox closed. Please use the Postal Cat Service.

    The next day, Leon put a backpack on each cat and dropped off the cats around the village. Leon knew that the cats would be happy lazing around all day. He also knew that they would always come home for dinner. Leon spent the day relaxing, waiting for his helpers to return. Leon was right. The cats did return, but they did not bring home many letters. Somehow, the cats had managed to wriggle（蜿蜒而行） out of their backpacks. Or lose their letters. Or get the letters wet. “Cats are just too unreliable（不可靠的）” Leon thought. Just then, there was a scratching（刮擦声） at Leon's door. A dog was waiting to be invited inside. That gave Leon an idea.

读《三棵树》，文中的“三棵树”是哪三棵树，各有什么特点？

当前，我国改革进入攻坚阶段，发展进入关键时期，必须以更大的政治勇气和智慧坚定不移推进改革开放，不失时机深化重要领域改革，破除一切妨碍科学发展的思想观念和体制机制弊端，不断推进我国社会主义制度的自我完善和发展。******在广东考察时强调，要“聚合各项相关改革协调推进的正能量”，“改革不停顿、开放不止步”。

运用历史唯物主义知识，说明为什么要“改革不停顿，开放不止步”。