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The range of radio 1______________ in space is extending more and more. There is every reason to believe that radio links may be set over 2________________ of 100 million kilometers or even more.
Now we cannot imagine our life without electronics.
But it all began with the 3_______________ of radio. It was our Russian scientist A.S. Popov who discovered the principles of wireless communication that finally led to the development of 4________________ tubes for use in various communication devices.