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构成核酸的基本单位是
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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 and programming. Given this information why do commercials sound so loudThe sensation of sound involves a variety of factors in addition to its speak level. Advertisers are skilful 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-frequency sounds can mask higher frequency sounds, advertisersfilter outany noises that may drown out the primary message. In addition, the human voice has more auditory (听觉的) impact in the middle frequency ranges. Advertisers electronically vary voice sounds so that they stay within such a frequency band. Another approach is to write the script so that lots of consonants are used, because people are more aware of consonants than vowel sounds. Finally, advertisers try to begin commercials with sounds that are highly different from those of the programming within which the commercial is buried. Because people become adapted to the type of sounds coming from programming, a dramatic change in sound quality draws viewer"s attention. For example, notice how many commercials begin with a cheerful song of some type.The attention-getting property of commercials can be seen by observing one-to two-year-old children who happen to be playing around a television set. They may totally ignore the programming. However, when a commercial comes on, their attention is immediately drawn to it because of its dramatic sound quality. Commercials create the sensation of loudness because ______.
患者关节微肿疼痛，活动不利，心悸气短，自汗，时有胸痛，失眠，纳差，乏力，舌质红，脉弱或细数。治宜选用
患者，男，40岁。症见多个关节疼痛，局部灼热、红肿，得冷少舒，痛不可触，苔黄燥，脉滑数。实验室检查：抗“O”>500U，C反应蛋白阳性，血常规示白细胞计数轻度升高，中性粒细胞稍增多。诊断为“风湿热”。治疗应首选
患者，女，56岁。患类风湿性关节炎12年，现低热，口苦，纳呆，关节肿痛以下肢为重，全身困乏无力，下肢沉重酸胀，有关节积液，舌苔黄腻，脉滑数。其证型是
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