[单项选择] Every year television stations receive hundreds of complaints about the loudness of advertisements. However, federal rules forbid the practice of making ads louder than the programming. In addition, television stations always operate at the highest sound level allowed for reasons of efficiency. According to one NBC executive, no difference exists in the peak sound level of ads programming. Given this information, why do commercials sound so loud The sensation of sound involves a variety of factors in addition to its speak level. Advertisers are skillful at creating the impression of loudness through their expert use of such factors. One major contributor to the perceived loudness of commercials is that much less variation in sound level occurs during a commercial. In regular programming the intensity of sound varies over a large range. However, sound levels in commercials tend to stay at or near peak levels. Other "tricks of the trade" are also used. Because low-frequenc
A. the human voices in commercials have more auditory impact
B. people like cheerful songs that change dramatically in sound quality
C. high-frequency sounds are used to mask sounds that drown out the primary message
D. they possess sound qualities that make the viewer feel that something unusual is happening