Which of the following statements are true concerning electromagnetic waves in a vacuum? Check all that apply

Electromagnetic waves travel in a vacuum with a definite and unchanging speed.
Electromagnetic waves can travel in a vacuum only because a medium prohibits the forward propagation of the electric and magnetic fields.
When electromagnetic waves travel in vacuum, there is a definite, constant ratio between the magnitudes of the electric and magnetic fields.
Electromagnetic waves traveling in a vacuum are longitudinal waves

Electromagnetic waves travel in a vacuum with a definite and unchanging speed.

When electromagnetic waves travel in vacuum, there is a definite, constant ratio between the magnitudes of the electric and magnetic fields.

Explanation:

Electromagnetic waves are waves that come about due to the vibrations generated between an electric field and a magnetic field. There is presence of oscillating magnetic and electric fields and the two statements mentioned above best describes it's properties.

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.