The answer is (b): the sound will get softer - in fact, the sound ceases entirely! Click your mouse on the photograph below see and hear the experiment.
The wire mesh acts as a Faraday cage for the radio waves, stopping the radio waves from entering the cage and getting to the radio. This mesh will be effective for all radio waves with wavelength somewhat longer than the spacing of the mesh.
So there was a purpose in putting the mesh over the radio: to shut up these over-enthusiastic sportscasters!
