为提高数据传输的可靠性，可采用“冗余校验”的方法；海明码是常用的方法之一。在此方法中，若要求能检测出所有的双位错，并能校正单位错，则合法码字集中的码距至少为 (127) 。若原始数据的字长为5位，则采用海明码时其校验位至少为 (128) 位。
对图1-22的图(a)所示系统，仅当部件1，部件2和部件3，全部正常工作时，系统才能正常工作。图中数字为各部件的可靠性，整个系统的可靠性近似为 (129) 。如果将部件2和部件3改成由两个器件构成，如图(b)所示，只要器件a和b中有一个正常就能使部件2正常工作，只要器件c和d中有一个正常就能使部件3正常工作。图中数字是各器件的可靠性，则部件2的可靠性是 (130) ，整个系统的可靠性近似为 (131) 。
128（）
A．1
B．2
C．3
D．4
参考答案：D
| Declan Mayes, President of the Music Buyers Association, is furious at a recent announcement by the recording industry regarding people downloading MP3 music files from the Internet as actual criminals. A few parallels may be instructive. If someone copies an audio music cassette for their own private use, they are, strictly speaking, breaking the law. But recording companies have usually turned a blind eye to this practice because prosecuting the few people involved would be difficult, and the financial loss to the company itself is not considered significant. Now the Music Recording Association has announced that it regards individuals downloading music from the Internet as pirates, claiming that they damage the industry in just the same way. "The industry is completely overreaching; it’ll be a laughing stock," says Mayes. "They’re going to arrest some teenager downloading files in his bedroom and sue him for thousands of dollars! This isn’t going to frighten anyone into buying CDs". Mayes may have a point. There is a general consensus that CD pirates should be subjected to the full wrath of the law, but few would see an individual downloading music for his or her own pleasure in the same light. However, downloading music files illegally is not as innocuous as making private copies of audio cassettes. The scratchy, distorted cassette copy is a poor version of the original recording, whereas an MP3 file is of high quality and can be stored on a CD, for example. It is this that makes the practice a powerful temptation for music fans, given the high cost of CDs. What does Mayes think about claims that music companies could be forced out of business by people downloading music illegally That’s nonsense. Music companies are always whining about high costs, but that doesn’t prevent them from recording hundreds of CDs by completely unknown artists, many of whom are "packaged" by marketing departments to appeal to young consumers. The companies are simply hoping that one of these new bands or singers will be a hit, and although it can be expensive to promote new artists, the cost of manufacturing the CDs is actually very low. This last point would appear to be the focus of resentment against music companies, a CD is far cheaper to produce than its price in the shops would indicate, and profit margins for the music companies are huge. An adult with a reasonable income may not object to paying ￡15 for a CD of classical music, but a teenager buying a CD by the latest pop sensation may find that price rather steep — especially since the latest pop sensation is almost certain to be forgotten within a few months. And while the recording industry can’t be held responsible for the evanescent nature of fame, given the teenage appetite for anything novel, it could lower the prices it charges — especially since technology is making CDs even cheaper to produce. This is what Mayes hopes will happen. If the music industry stops exploiting the music-buying public, it can survive. Everyone would rather buy a CD, with an attractive jacket and booklet, than mess around downloading files, but the price has to be reasonable. The problem isn’t going to vanish if the industry carries on trying to make a quick profit. Technology has caught up with the music companies, and trying to fight it by taking people to court will only earn money for the lawyers. |
According to the passage, Mayes implies that music companies______.
A．(A) could cut costs by making cheaper CDs
B．(B) should not promote artists who are unknown
C．(C) are speculating when they promote new artists
D．(D) should use different manufacturing processes