已知线段a，b，c，求作△ABC，使BC=a，AC=b，AB=c．①以点B为圆心，c为半径圆弧；②连接AB，AC；③作BC=a；④以C点为圆心，b为半径画弧，两弧交于点A．作法的合理顺序是 ____

阅读理解

    Mother Teresa was born on August 26^th,1910 in Skopje, Macedonia. She always wrote her birthday as 27^th of August because it was the day of her baptism(洗礼), which was always more important to her than her birthday. For her work with the poor around the world, she received the 1979 Nobel Peace Prize.

    In 1928, she accepted a religious order and took the name Teresa. The order immediately sent her to India. A few years later, she began teaching in Calcutta. In 1948 the Catholic(天主教的) Church agreed her request and let her enter the convent(女修道院) and she began to work for the poor people. She became an Indian citizen in the following year. In 1950, she set up a religious organization in Calcutta. The organization provided food for the poor people and then she set up hospitals, schools, youth centers, and homes for the sick and the dying poor. It now has branches in 50 Indian cities and 30 other countries.

    Besides the 1979 Nobel Peace Prize, Mother Teresa has received other awards for her work with the poor people. On September 5^th,1997, Mother Teresa passed away, but she will continue to inspire people all over the world through her lasting present of love and faith.

如图所示，弹簧所受重力不计，上端固定在天花板上，下端悬挂一小球，处于静止状态．下列几对力中属于平衡力的是（   ）

【节能环保 促发展】

材料一：近期，我国部分地区再度收到雾霾困扰。据中国环境监测总站研究员宫正宇介绍，10月1日至今，全国发生了三次较大范围的区域性灰霾污染过程，161个城市共发生155天次重度污染和31天次严重污染。

材料二：在一些地区，由于地下水位下降，去年才打的井，已抽不出水来浇灌龟裂的田地。有村民无奈地说，满地井眼，没有一个出水的。这既是面对旱情的无奈悲叹，也是农业水危机的真实写照。

材料三：近年来，国际上提出了“循环经济”的新概念，循环经济倡导的是建立在生活不断循环利用基础上的发展模式。上海宝钢通过采用先进工艺技术和强化管理，使水的重复利用率达98%。