It is basically shielding a magnetic field. This can be done with rubber or any other material that is thick. Normally small magnets already block the shield.
Answer: The correct answer is a.
Explanation:
Electromagnetic wave is a wave in which the magnetic field and the electric field are perpendicular to each other.
Both fields are directed in the direction of the propagation of the electromagnetic wave. It travels with the speed of the light.
The motion of the electric field produces both electric field and the magnetic field.
The electromagnetic waves are produced when an electric charge vibrates or accelerates.
Therefore, the correct option is (a).
From Greek meaning not divisible.
Answer
The wavelength for 550 kHz signal is

λ = 545.45 m
The wavelength for 1600 kHz signal is

λ = 187.5 m
The wavelength for 88 MHz signal is

λ = 3.41 m
The wavelength for 108 MHz signal is

λ = 2.78 m