下列物质属于单质的是（　　）

材料一：2017年12月4日是我国现行宪法颁布施行3 5周年纪念日，也是第17个全国法制宣传日暨国家宪法日。为深入贯彻落实******在首都各界纪念现行宪法公布施行3 5周年大会上的重要讲话精神，司法部、教育部、共青团中央、全国普法办在北京市宏志中学举办了“宪法进课堂”活动。

材料二：2018年3月11日，十三届全国人大一次会议在北京人民大会堂举行第三次全体会议，代表投票表决中华人民共和国宪法修正案草案。

材料三：十三届全国人大一次会议还将审议《中华人民共和国监察法（草案）》。夺取反腐败斗争压倒性胜利，治本之策在于加强对权力的监督。构建党统一指挥、全面覆盖、权威高效的监督体系，将进一步加强对权力运行的制约和监督，实现对所有行使公权力的公职人员监察全覆盖。

为了普及宪法和法律知识，八年级11班准备开展一次活动，请你参与：

    Baron Pierre de Coubertin was a Frenchman. At his time sports were not taught in French schools. De Coubertin believed that sports should go hand in hand with studies. He had an idea. His idea was to begin the Olympics all over again.

    Sports teachers of other countries liked De Coubertin ideas. So in 1896, the modern Olympic Games were held in Athens, Greece. Since then the Olympics have been held once every four years, except three times, when there were wars.

    The modern Olympic games have many foot races and field sports programs. The longest race in the games is called marathon（马拉松）.

    Before the start of the Olympic Games, runners carry lighted torch(火炬) through many nations towards the stadium（体育场 ）where the games will be held. These sportsmen are from different countries. Yet they work together to carry the Olympic torch. It is passed from runner to runner,  When the last runner enters the stadium, he or she places the torch in a special basin filled with oil. It catches fire. It is then, only then, that the Olympic Games can begin.

    The Olympic flame（火焰）burns throughout the games. It is the flame of peace.