单项选择题

Psychologists now believe that noise has a considerable effect on people’s attitudes and behavior. Experiments have proved that in noisy situations (even temporary ones ), people behave more irritably and less cooperatively; in more permanent noisy situations, many people cannot work hard, and they suffer from severe anxiety as well as other psychologecal problems. However psychologists distinguish between“sound”and “noise”.“Sound”is measured physically in decibels.“Noise”cannot be measured in the same way because it refers to the psychological effect of sound and its level of “intensity”depends on the situation. Thus, for passengers at an airport who expect to hear airplanes taking off and landing, there may be a lot of sound, but not much noise (that is, they are not botered by the noise). By contrast, if you are at a concert and two people behind you are whispering you feel they are talking noisily even if there is not much sound. You notice the noise because it affects you psychologically. Both sound and noise can have negative effects, but what is most important is if the person has control over the sound. People walking down the street with earphones listening to music that they ecjoy, are receiving a lot of decibels of sound, but they are probably happy hearing sounds that they control. On the other hand, people in the street without earphones must tolerate a lot of noise which they have no control over. It is noise pollution that we need to control in order to help people live more happily.

Sound, as defined by the psychologist, （）