《九章算术》是中国传统数学最重要的著作，奠定了中国传统数学的基本框架．其中卷第九勾股，主要讲述了以测量问题为中心的直角三角形三边互求的关系．其中记载：“今有邑，东西七里，南北九里，各中开门，出东门一十五里有木，问：出南门几何步而见木？”

译文：“今有一座长方形小城，东西向城墙长7里，南北向城墙长9里，各城墙正中均开一城门．走出东门15里处有棵大树，问走出南门多少步恰好能望见这棵树？”（注：1里=300步）

你的计算结果是：出南门____ 步而见木．

    It is Saturday morning. The sky is blue. My father and I are going to the park. There are a lot of people in the park. Some children are running on the grass. A dog is running after them. Some men are sitting on the grass. They are talking. Two girls are flying a nice kite. Three women are standing under a tree, and they are watching the children playing. There is a boat in the lake and two women are boating. Everyone in the park is very happy.

要使分式$\frac{1}{x-1}$有意义，x的取值范围满足（　　）

我国是世界上最大的发展中国家，复兴之路上取得了举世瞩目的成就。但是发展中还是面临很多挑战，下列哪个不属于面临的挑战 （   ）