# Surface wave propagation is done near the surface of earth.Surface wave propagation is sutable upto

$\begin{array}{1 1}(a)\;\text{upto 100MHz}\\(b)\; \text{upto 20MHz}\\(c)\;\text{above 100MHz}\\(d)\;\text{above 20MHz}\end{array}$

The surface wave propagation is suitable for low and medium frequency upto 20MHz only.
Hence (b) is the correct answer.