Final answer:
The constancy of the speed of light challenges traditional concepts of velocity and reference frames.
Step-by-step explanation:
The correct option is B) The constancy of the speed of light challenges traditional concepts of velocity and reference frames.
The speed of light is unique in that it is always constant, regardless of the motion of the source or the observer. This means that no matter how fast or slow an observer is moving, they will always measure the speed of light to be the same value.
This concept, known as the constancy of the speed of light, challenges traditional ideas about velocity and reference frames, where objects moving at different speeds would have different observed velocities. It is a fundamental principle of Einstein's theory of relativity.