The electric field measured in the far field of an antenna at a distance of 50m is 1V/m. The average power densities at a distance of 500m from the antenna is

A

$$ 26.6 \mu W/m^2 $$

B

$$ 0.1 \mu W/m^2 $$

C

$$ 10 \mu W/m^2 $$

D

$$ 13.3 \mu W/m^2 $$