Answer:
c. Electromagnetic waves do not always need a medium to travel.
Explanation:
As the name suggests Electromagnetic waves consist of Electric and Magnetic fields.
Electromagnetic waves are transverse waves.
In a given medium Electromagnetic waves cannot vary in speed. However their wavelength and frequency can vary.
When an Electromagnetic wave travels through a medium It does not displace the medium. So, electromagnetic waves do not need a medium to travel.
