根據下面的文字資料回答 71～75 題In the following essay，each blank has fourchoices．Choose the best answer and write down on thean，swer sheet．

Microwave communication uses（ 1 ）frequency radio waves that travel instraighdine sthroughthe air．Because the waves cannot（ 2 ）with the curvature of the earth，they can be （ 3 ）onlyover short distance．Thus，microwave is a good（ 4 ）for sending data between bulldingsin a city or on a large college campus．For longer distances，the waves must berelayed by means of“dishes”or（ 5 ）．These can be installed on towers，highbuildings，and mountain tops．

第71題：文中（ 1 ）處正確的答案是（ ）。

A．high

B．10w

C．1ong

D．short

A微波通信利用在空氣中直線傳播的高頻無線電波通信，因為電磁波不能隨著地球表面的曲度而彎曲，所以只能用來在短距離內傳輸。這樣，微波就是一種在大樓之間或在大的大學校園里用來發送數據的優良介質。如果要進行更長距離的傳輸，電磁波必須通過蝶行衛星天線或普通天線中轉。這些天線能夠被安裝在塔頂、高樓和山頂上。