Final answer:
The correct answer is that for special relativity to describe an object's movement, the object must be moving at a constant speed in a straight line (inertial motion). The speed of light is also constant in all inertial frames of reference according to special relativity.
Step-by-step explanation:
The object must be moving in a way that allows us to apply the theory of special relativity to describe its movement. The correct answer is B: The object must be moving at a constant speed in a straight line; how fast it is moving is not important. Special relativity applies to inertial frames of reference, which are frames of motion where objects either remain at rest or continue to move at a constant speed in a straight line unless acted upon by an outside force. This corresponds with Einstein's first postulate of special relativity, which states that the laws of physics are identical in all inertial frames of reference. The second critical aspect of special relativity is the constancy of the speed of light, which implies that the speed of light is always the same in all inertial frames of reference, regardless of the motion of the light source or the observer.