题目

阅读下面的短文，并从下列方框里的六个句子中选择五个还原到原文中，使原文的意思完整，连贯。You may see people in need on the news after a typhoon. Perhapsyou've walked past homeless people on the streets. Or maybe you've come acrosslost dogs and wished you could give them a home. Theanswer is to be volunteers! Volunteering means spending some of your free timeand energy to help others. December 5'is International Volunteer Day. It calls for people around the world to volunteer to helpthose in need. People volunteer to help others in many ways. Volunt（2.5分）我们常通过化学反应来认识物质的化学性质。氢气具有可燃性，化学方程式为：         ，基本反应类型是         反应；氢气具有还原性，可以和CuO反应，化学方程式为：H2+CuO Cu + H2O。我们常从元素化合价的变化来认识氧化——还原反应：在化学反应中，只要有元素化合价升高的反应物就具有还原性。上述两个反应中，氢元素的化合价都从  价变成  价，都能体现氢气具有还原性。从元素化合价的变化特点来分析，在下列四个反应中，能体现金属铁具有还原性的反应有         （填字母代号）。A．3Fe + 2O2Fe3O4B．Fe + 2FeCl3 ==== 3FeCl2　 C．3CO + Fe2O3 2Fe+ 3CO2D．Fe + CuSO4 ==== FeSO4 + Cu