One reason human beings can thrive in all kinds of climates is that they can control the q

ualities 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】

A．achieve

B．avail

C．amount to

D．assign