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 (1) that control in such places (2) homes, offices, theaters, institutions, factories, airplanes, and automobiles. The most familiar type of air conditioning is summertime cooling. Although important, this is (3) one of several aspects of air conditioning. Other applications (4) . the control of the humidity (or air moisture), cleanliness, circulation of the air, and heating.
Tests have (5) that people generally feel best (6) certain temperature, humidity, and air velocity conditions. Temperatures can (7) from 21.5° C with 70 percent relative humidity to 28° C with 30 percent relative humidity. Relative humidity is the (8) of moisture in the air (9) a specific temperature compared A. determined
B. caused
C. maintained
D. achieved
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