Which one of the following statements is wrong?

Options

A. Radio waves in the frequency range 30Hz to 60MhZ are called sky waves.
B. Radio horizon of the transmitting antenna for space wave is `d_r=sqrt((Rh_r))`
C. Within the help distance neither the ground waves nor the sky waves are received
D. The principle of fibre optical is free from electrical disturbances.

Answer

A