One reason human beings can thrive in all kinds of climates is that they can control the qualities of the air in the enclosed spaces in which they live. Air conditioning is the use of mechanical systems to 【C1】______ that control in such places 【C2】______ homes, offices, theaters, institutions, factories, airplanes, and automobiles. The most familiar type of air conditioning is summertime cooling., Although important, this is 【C3】______ one of several aspects of air conditioning. Other applications 【C4】______ the control of the humidity (or air moisture), cleanliness, circulation of the air, and heating. Tests have 【C5】______ that people generally feel best 【C6】______ certain temperature, humidity, and air velocity conditions. Temperatures can 【C7】______ from 21.5°C with 70 percent relative humidity to 28°C with 30 percent relative humidity. Relative humidity is the 【C8】______ of moisture in the air 【C9】______ a specific temperature compared 【C10】______ the amount it could hold at that temperature. 【C11】______ air velocities range from 4.5 to 10.5 meters per minute. It is also desirable that an air conditioner 【C12】______ dust, pollen, smoke, and odors from the air. In many industrial environments, air conditioning is essential. Most print shops, for example, 【C13】______ . constant humidity in order to control paper shrinkage and 【C14】______ the 【C15】______ operation in some processes. Libraries, especially ones With rare books, require air control to 【C16】______ the physical quality of their collections. Bakeries and the tobacco and cotton industries require high humidity 【C17】______ their products, and perishables such as fruits must be stored in cool, dry rooms. Some electronic components, drugs, and chemicals must be manufactured 【C18】______ the air is as free as possible 【C19】______ dust and other particles. Air conditioning is 【C20】______ in hospitals, especially in operating rooms. 【C1】