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  3. The new global satellite communications systems will offer three kinds of service, which may overlap in many different kinds of

The new global satellite communications systems will offer three kinds of service, which may overlap in many different kinds of

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问题     The new global satellite communications systems will offer three kinds of service, which may overlap in many different kinds of receivers.
    VOICE. Satellite telephones will be able to make calls from anywhere on the earth to anywhere else. That could make them especially useful to remote, third world villages (some of which already use stationary satellite telephones), explorers and disaster-relief teams. Today’s mobile telephones depend on earth-bound transmitters, whose technical standards vary from country to country. So business travelers cannot use their mobile phones on international trips Satellite telephones would make that possible.
    MESSAGING. Satellite massagers have the same global coverage as satellite telephones, but carry text alone, which could be useful for those with laptop computers. Equipped with a small screen like today’s papers, satellite messages will also receive short messages.
    TRACKING. Voice and messaging systems will also tell their users where they are to within a few hundred meters. Combined with the messaging service, the location service could help rescue teams to find stranded adventurers, the police to find stolen cars, ex- porters to follow the progress of cargoes, and haulage companies to check that drivers are not detouring to the pub. America’s military Global Positioning System(GPS) satellites will provide better positioning information to anyone who has a receiver for their signals, but GPS does not carry messages, so such a receiver cannot be used on its own for tracking or rescue. By the mid-1990s, GPS receivers will be able to tell people where they are to within 70 meters anywhere in the world, and to within a meter or so in areas where the service is supplemented by ground-based transmitter.
选项 A、laptop computer users
B、remote villages
C、disaster-relief teams
D、all above
答案D
解析
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