A Repeater Is Frequently Used as a Component During Emergency

A repeater is frequently used as a component during emergency communication systems because

A) very high frequencies and low-band frequencies can both be stopped by solid structures.
B) low-band frequencies are subject to interference by atmospheric conditions and electrical equipment.
C) ultrahigh frequencies travel in a straight line but they have a short range communication distance.
D) very high frequencies travel in a straight line but they cannot penetrate solid structures.