根據(jù)下面的文字資料回答 71~75 題In the following essay,each blank has fourchoices.Choose th
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
正確答案: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(xué)校園里用來發(fā)送數(shù)據(jù)的優(yōu)良介質(zhì)。如果要進(jìn)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。
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