ANS:D - SHF

Because for a signal to escape earth it has to have frequency above 250 MHz. Anything less than that will be reflected back to earth or absorbed by the ionosphere.VHF is below 3 to 300 MHz.

Now that leaves us with three choices UHF SHF and EHF.

UHF is used for mobile communications. EHF is difficult to generate and requires lot of power to operate. So, SHF is only frequency range which is economical and viable.