根据下面资料，回答21-25题
Digital Video Express
①A pay-for-play system for video DVD will emerge by summer as an alternative, and possibly a competitor, to the DVD format currently available.
②The new system, called Digital Video Express( Divx), operates like a DVD player, except
for the specially coded discs. These will cost $5 for initial viewing over a 48-hour period and can be viewed again for additional fees and even purchased for unlimited viewing.
③Divx combines the service of a video rental( 出租的)store with the operation of a pay-per-view channel. Unlike a rented videotape, though, the Divx disc needn't be returned. Customers can retain the disc for replay in the future at an additional fee, or simply throw it away.
④Subsequent plays,or the purchase of unlimited-viewing rights, are billed to the customer's Divx account and charged to a credit card. The player' s built-in memory keeps track of all Divx plays, and sends this information by toll-free phone modem(调制解调器) to the Divx record-keeping centre. Each Divx disc and player has a unique identification code, so the system knows which discs have been played and where.
⑤Some Divx discs could be converted for unlimited play at a price likely to be lower than buying a conventional DVD. Others, called Divx Gold, would be sold from the beginning for unlimited play without further charge. Although conventional DVDs will run in a Divx player, conventional DVD players will lack the decoding (解码) and communications ability to play Divx discs. Divx players will be offered by Panasonic, RCA, and Zenith.

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