An antenna is 30 metre high. The frequency is 1 MHz. The radiation resistance is about-A-1500 ΩB-150 ΩC-15 ΩD-1.5 Ω-C-15 Ω

C 15 Ω Rrad = 160(π*height/wavelength)^2. Wavelength = 300m, Height = 50, Rrad= 15.8 ohm.