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买入A交易所5月铜期货合约，同时卖出B交易所5月铜期货合约

买入A交易所5月铜期货合约，同时买入A交易所7月铜期货合约

买入A交易所5月铜期货合约，同时卖出A交易所7月铜期货合约

买入A交易所5月铜期货合约，同时买入B交易所5月铜期货合约

买入A交易所5月铜期货合约，同时买入A交易所7月铜期货合约

买入A交易所5月铜期货合约，同时卖出A交易所7月铜期货合约

买入A交易所5月铜期货合约，同时卖出B交易所7月铜期货合约

买入A交易所5月铜期货合约，同时买入B交易所7月铜期货合约

正确

错误

血清病

结核菌素肉芽肿

青霉素过敏反应

新生仔畜溶血性贫血

自身免疫复合物病

Since moving pictures were invented a century ago，a new way of distributing entertainment to consumers has emerged about once every generation．Each such innovation has changed the industry irreversibly；each has been accompanied by a period of fear mixed with exhilaration．The arrival of digital technology, which translates music．pictures and text into the zeros and ones of computer language，marks one of those periods．

This may sound familiar, because the digital revolution，and the explosion of choice that would go with it, has been heralded for some time．In 1992，John Malone，chief executive of TCI，an American cable giant．welcomed the '500-channel universe'．Digital television was about to deliver everything except pizzas to people's living rooms．When the entertainment companies tried out the technology, it worked fine-but not at a price that people were prepared to pay． C Those 500 channels ually arrived but via the Internet and the PC rather than through television．The digital revolution was startinq to affect the entertainment business in unexpected ways．ually it will chanqe every aspect of it，from the way cartoons are made to the way films are screened to the way people buy music．That much is clear．What nobody is sure of is how it will affect the economics of the business．

New technologies always contain within them both threats and opportunities．They have the potential both to make the companies in the business a great deal richer, and to sweep them away．Old companies always fear new technology．Hollywood was hostile to television，television terrified by the VCR．Go back far enough，points out Hal Varian．an economist at the University of California at Berkeley, and you find publishers complaining that' circulating libraries' would cannibalise their sales．Yet whenever a new technology has come in，it has made more money for existing entertainment companies. The proliferation of the means of distribution results，gratifyingly, in the proliferation of dollars，pounds， pesetas and the rest to pay for it.

All the same，there is something in the old companies' fears．New technologies may not threaten their lives．but they usually change their role．Once television became widespread，film and radio stopped being the staple form. of entertainment．Cable television has undermined the power of the broadcasters．And as power has shifted the movie studios，the radio companies and the television broadcasters have been swallowed up．These days，the grand old names of entertainment have more resonance than power．Paramount is part of Viacom，a cable company; Universal，part of Seagram, a drinks-and-entertainment company; MGM，once the roarinq lion of Hollywood，has been reduced to a whisper because it is not Dart of one of the giants．And RCA，once the most important broadcasting company in the world，is now a recording label belonging to Bertelsmann，a large German entertainment company． &n

血清病

青霉索过敏反应

结核菌素肉芽肿

新生畜溶血性贫血

自身免疫复合物病