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参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】It is now almost two years since the European Union decided to go ahead with plans to launch a satellite-navigation network to rival America’s existing Global Positioning System (GPS). For much of thi...
A.
Using of various signals for communication.
B.
Writing message or information in secret code.
C.
Automatic ally operated positioning system.
D.
Accuracy checking device.