Write two factors which justify the need of modulating a low frequency signal into high frequencies before transmission

The required two factors are -
a) The transmission of the low-frequency signal needs an antenna of height 4-5 km which is impossible to construct. So we need to modulate wave in order to reduce the height of the antenna .
b) The effective power radiated by the antenna will be as P∝λ². Thus, for effective radiation by an antenna, we need to modulate the wave.