Volunteering to help people in need combined____travelling to faraway places is ____ new trend in the travel industry. It is called voluntourism. People travel to other countries, learn languages and other cultures and gain new____ ( experience ). Recent statistics show that in the past few years voluntourism ____ ( be) one of the fastest - growing areas of tourism, More than 1.6 million people around the world are volunteers in other countries. They work in orphanages (孤儿院), help build schools, assist in hospitals and do farming work in____ (develop) countries. There are many reasons ____ people want to engage in voluntourism, Students see it as a gap year after school, while others ____ (simple) want to take time out from a job and do something else. However, some voluntourists do not see volunteering ____ what it is. They only think it is a cheap way ____（travel）and don't really want to get____ （involve） in hard work.

在各种新型材料的研发、制造和使用中，有涤纶、腈纶等各种____（填“天然”或“合成”）纤维制成的五彩缤纷的衣料；有汽车等交通工具的轴承以及刀具等所用到的各种____（填“金属”或“非金属”）材料。在农业生产中，化肥通常可分为氮肥、____和磷肥。肥田粉的主要成分是硫酸铵，它属于____肥。制造普通玻璃的原料是纯碱 石灰石 石英，反应原理是碳酸钠 碳酸钙在高温下分别跟石英反应生成硅酸盐（CaSiO₃）.写出这两个反应的化学方程式：①____；②____。