问题
单项选择题
Microwave communication uses high-frequency (71) waves that travel in straightlines throughthe air. Because the waves cannot (72) with the curvature of the earth, they can be (73) only over short distance. Thus, microwave is a good (74) for sendingdata between buildings ina city or on a large college campus. For longer distances, the wavesmust be relayed by means of"dishes" or (75) . These can be installed on towers, highbuildings, and mountain tops.
A．repeaters
B．radars
C．telephones
D．antennas
答案
参考答案：D
解析：微波通信使用高频的无线(radio)电波，它在空气中沿直线传播。由于这种波不会随地面弯曲而弯曲(benD)，它仅能在短距离内传播(transmitteD)。因此微波是在城市的建筑间或在一个大的大学校园内传输数据的良好介质(medium)。对于较长距离来说，这种波必须用“盘子”或者说天线(antennas)进行中继。这些设备可以被安装在塔、高层建筑或山的项部。