[单项选择]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.【C7】
A. alter
B. range
C. differ
D. move