The correct answer to the question is - A). Light waves can travel in a vacuum and travel at a constant speed even if the light source is moving.
EXPLANATION:
Before going to answer this question, first we have to understand the fundamental postulate of quantum mechanics.
As per the fundamental postulate of quantum mechanics, the speed of light is always constant irrespective of the nature of frame of reference i.e speed of light is same both in inertial and non-inertial frame of reference. It is independent of the velocity of source also.
Again we know that light is an electromagnetic wave. Hence, it won't require any medium for its propagation. It can travel in space or vacuum also.
Hence, the correct option out of four options is that light waves can travel in a vacuum and travel at a constant speed even if the light source is moving.
