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 writedown on the answer sheet．
Microwave communication uses high—frequency（ 1 ）waves that travel in straightlines through the air．Because the waves cannot（ 2 ）with the curvature of the earth，theycan be（ 3 ）0nly over short dis- tance．Thus，microwave is a good（ 4 ）for sendingdata 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：