Microwave communication uses high-frequency (1)______ waves that travel in straightlines throughthe air. Because the waves cann

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问题 Microwave communication uses high-frequency (1)______ waves that travel in straightlines throughthe air. Because the waves cannot (2)______with the curvature of the earth, they can be (3)_____only over short distance. Thus, microwave is a good (4) ______for sendingdata between buildings ina city or on a large college campus. For longer distances, the wavesmust be relayed by means of"dishes" or (5)_____. These can be installed on towers, highbuildings, and mountain tops.
(4)______
A．material
B．equipment
C．medium
D．Channel

选项 A、
B、
C、
D、

答案C

解析

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