小华和同学捡到一块动物的骨头，他们判断这是鸟的骨骼．他们作出判断的依据是这块骨（　　）

根据短文内容回答下列各问题。

    Ma Hua graduated from Fudan University. He had a good career in IT and a great life in Shanghai, but he felt there was something missing from his life. He wanted to help others to improve their lives, so in March 2013 he gave up his job. Then he moved to south-west China to do voluntary work in a village primary school.

    He soon became an important member of the local people. In his class, he painted pictures on the walls to help students remember English words. He also spent his money building a playground for the children.

    Ma Hua quickly got used to his new life. He got great satisfaction(满意) from his work and felt very happy, even though life there was hard---he had to melt(融化) ice for water and grow vegetables for food. When he was free, he wrote poems describing the peace and beauty around him. Sometimes he would go walking in the mountains and enjoy the beautiful view. Sadly Ma Hua was killed in a car accident in July 2014 at the age of 31. His death was a great loss to all those who knew him, but it is a comfort to know that he lived happily, doing what he loved and enriching the lives of others.

“绝圣弃智，民利百倍；绝仁弃义，民复孝慈；绝巧弃利，盗贼无有。”又说：“甘其食， 美其服，安其居，乐其俗。使民复结绳而用之。”这主要反映了先秦时期（  ）

实数a在数轴上的位置如图所示，则下列说法正确的是（　　）

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