Electromagnetic waves

A.     always obey an inverse square law.

B.     are made up of electric and magnetic fields of constant amplitude.

C.     always travel at the same speed in a vacuum.

D.     are always polarized.

C

Anything that radiates outwards from a point source will obey the inverse square law, whether it be gravity, magnetism from a monopole, warmth or light. But there are situations when an electromagnetic wave does not radiate equally in all directions – as, for example, with a laser. So C is the correct response.