In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.
Microwave communication uses high-frequency (26) waves that travel in straightlines through the air. Because the waves cannot (27) with the curvature of the earth, they can be (28) only over short distance. Thus, microwave is a good (29) for sendingdata between buildings in a city or on a large college campus. For longer distances, the waves must be relayed by means of "dishes" or (30) . These can be installed on towers, high buildings, and mountain tops.

A．optical

B．radio

C．electrical

D．magnetic

下列有关汽车SRS系统的叙述为错误（）

A.驾驶装备SRS系统的车辆上高速公路时一定要系上安全带

B.装备SRS系统的车辆如不系安全带，在发生撞击时气将不爆出，以免了现误伤

C.有些车型的SRS系统装备有专用的备用电源

D.SRS系统的故障代码的消除方法与汽车上其它电控系统工程有明显不同