根據(jù)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(nèi)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(fā)送數(shù)據(jù)的優(yōu)良介質(zhì)。如果要進行更長距離的傳輸，電磁波必須通過蝶行衛(wèi)星天線或普通天線中轉(zhuǎn)。這些天線能夠被安裝在塔頂、高樓和山頂上。