People build many different kinds of shelter throughout the world. The types of shelters they erect depend 16_______ on the climate and on what building materials are 17_______ . In hot areas, the weather is warm enough for people to live 18 _______ much of the time. But they still need protection 19 _______ sun, rain, and insects. Houses there have many screened windows, doors, and other openings that let in breezes but keep out insect pests. In the cool regions, houses are 20 _______ to keep out the cold and keep in heat. Many buildings have thick walls to 21 _______ heat loss. In such snowy countries as Norway and Sweden, people build houses with sloping roofs 22_______ snow will slide off easily. Building methods and materials 23_______ widely throughout the world. In regions with large forests, many people use wood to build homes. 24_______ is easy to build with, but most wooden buildings are less sturdy than those made of stone or concrete. In areas with little 25_______ ,people construct many shelters of clay or mud. In Mexico and the southwestern United States, for example, people 26_______ clay and dirt or mud with water to make adobe （砖坯）. In wet tropical areas, 27_______ causes wood shelters to rot within a few years. People in these areas build houses from other materials. For example, in some parts of Africa and on many Pacific islands, people weave the 28_______ of tall grass into houses. High-rise buildings made of steel and concrete are most common in such industrial countries as the United States and Canada. Prefabricated buildings 29_______ parts manufactured at a factory and then shipped to the construction_______ 30 . There construction workers assemble the parts. Many prefabricated shelters use large amounts of plastic and other lightweight materials.______