5) Which of the following statements are true concerning electromagnetic waves in a vacuum?
A) Electromagnetic waves can travel in a vacuum only because a medium prohibits the forward propagation of the electric and magnetic fields.
B) Electromagnetic waves traveling in a vacuum are longitudinal waves, like sound waves.
C) Electromagnetic waves travel in a vacuum with a definite and unchanging speed.
D) Electromagnetic waves travel in a vacuum with an indefinite and constantly changing speed.