题目内容：
根据下列题干，回答题：In the following essay，each blank has four choices．Choose the best answer and write down on the answer sheet．
Microwave communication uses（ 1 ）-frequency radio waves that travel in straightline sthrough the 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 sending data between buildings in a 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．
请选择（1）处最佳答案：
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答案解析：